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RBSE Secondary Science study materials
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RBSE Secondary Science practice questions

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Question 1Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which gas is produced when a dilute acid reacts with an active metal such as zinc?

  1. Carbon dioxide
  2. Chlorine
  3. Oxygen
  4. Hydrogen Correct answer.

Explanation

When a dilute acid reacts with a metal that lies above hydrogen in the reactivity series, the metal displaces hydrogen ions from the acid and hydrogen gas is released. This gas burns with a characteristic pop sound, which is used as a simple test for it. Oxygen, carbon dioxide and chlorine are not produced in this reaction.

Question 2Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

A solution has a pH of 3. Which statement about this solution is correct?

  1. It is acidic and turns red litmus blue
  2. It is neutral and has no effect on litmus
  3. It is alkaline and turns red litmus blue
  4. It is acidic and turns blue litmus red Correct answer.

Explanation

A pH below 7 indicates an acidic solution, and acids turn blue litmus paper red. A pH of 3 therefore means the solution is acidic, not neutral or alkaline. Alkaline solutions have pH above 7 and turn red litmus blue.

Question 3Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement correctly describes a displacement reaction between two metals?

  1. A less reactive metal displaces a more reactive metal from its salt solution
  2. Both metals dissolve equally in the salt solution
  3. Neither metal reacts because both are solids
  4. A more reactive metal displaces a less reactive metal from its salt solution Correct answer.

Explanation

In a displacement reaction a more reactive metal takes the place of a less reactive metal in its compound. For example, zinc displaces copper from copper sulphate solution because zinc is higher in the reactivity series. The reverse reaction does not occur.

Question 4Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which of the following is the general formula of an alkane?

  1. CnH2n
  2. CnH2n+2 Correct answer.
  3. CnH2n+1OH
  4. CnH2n-2

Explanation

Alkanes are saturated hydrocarbons in which every carbon atom forms four single bonds, giving the general formula CnH2n+2. Methane, CH4, and ethane, C2H6, both fit this pattern. The other formulas describe alkenes, alkynes and alcohols.

Question 5Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

In the modern periodic table, elements are arranged mainly in order of increasing what?

  1. Number of neutrons
  2. Atomic number Correct answer.
  3. Density
  4. Atomic mass

Explanation

Mendeleev arranged elements by atomic mass, but the modern periodic table places them in order of increasing atomic number. This ordering explains the repetition of chemical properties because it reflects the arrangement of electrons. Density and neutron number do not determine position.

Question 6Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which product is formed when dilute hydrochloric acid reacts with sodium hydroxide solution?

  1. Sodium chloride and hydrogen
  2. Sodium oxide and water
  3. Sodium hydroxide and chlorine
  4. Sodium chloride and water Correct answer.

Explanation

The reaction between an acid and a base is neutralisation, and it produces a salt plus water. Hydrochloric acid supplies chloride ions and sodium hydroxide supplies sodium ions, so the salt formed is sodium chloride. No gas is released in this reaction.

Question 7Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which non-metal is a good conductor of electricity in its solid form?

  1. Iodine
  2. Graphite Correct answer.
  3. Sulphur
  4. Phosphorus

Explanation

Graphite is an allotrope of carbon in which each carbon atom is bonded to three others, leaving one delocalised electron per atom to carry current. This makes graphite a conductor even though it is a non-metal. Sulphur, phosphorus and iodine do not conduct electricity.

Question 8Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which type of reaction is represented by the equation CaCO3 -> CaO + CO2?

  1. Neutralisation
  2. Combination
  3. Thermal decomposition Correct answer.
  4. Displacement

Explanation

A single compound, calcium carbonate, breaks down into two simpler substances when heated strongly. This is a thermal decomposition reaction. No acid-base neutralisation, metal displacement or joining of substances is involved.

Question 9Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which observation shows that a chemical reaction has taken place when iron nails are placed in copper sulphate solution?

  1. The blue colour fades and a reddish-brown deposit forms on the nails Correct answer.
  2. The solution becomes more intensely blue
  3. A colourless gas bubbles off rapidly
  4. The nails become shiny and silver coloured

Explanation

Iron is more reactive than copper, so it displaces copper from copper sulphate solution. The blue colour of copper ions fades as they are removed, and reddish-brown copper metal deposits on the iron. This is a displacement reaction.

Question 10Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

A student adds magnesium ribbon to dilute sulphuric acid. Which pair of products is formed?

  1. Magnesium sulphate and oxygen
  2. Magnesium sulphate and hydrogen Correct answer.
  3. Magnesium oxide and hydrogen
  4. Magnesium sulphide and water

Explanation

A reactive metal reacting with a dilute acid gives a salt and hydrogen gas. Here the metal is magnesium and the acid is sulphuric acid, so the salt is magnesium sulphate and the gas is hydrogen. Oxygen and sulphur-containing products are not formed.

Question 11Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which oxide reacts with both dilute acid and dilute alkali, showing amphoteric behaviour?

  1. Carbon dioxide
  2. Sodium oxide
  3. Magnesium oxide
  4. Aluminium oxide Correct answer.

Explanation

An amphoteric oxide can act as an acid with bases and as a base with acids, and aluminium oxide is a classic example. It dissolves in both dilute hydrochloric acid and sodium hydroxide solution. Sodium oxide and magnesium oxide are basic, while carbon dioxide is acidic.

Question 12Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which property of a homologous series stays the same for all its members?

  1. Number of carbon atoms
  2. Boiling point
  3. General method of preparation and chemical properties Correct answer.
  4. Molecular mass

Explanation

Members of a homologous series share a general formula and similar chemical properties, and they can be prepared by related methods. Molecular mass, boiling point and carbon number all increase steadily along the series. The shared chemical behaviour is what defines the series.

Question 13Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Ethanoic acid is a weak acid. What does this mean in terms of its behaviour in water?

  1. It is completely ionised, giving a high concentration of hydrogen ions
  2. It produces hydroxide ions when dissolved
  3. It does not dissolve in water at all
  4. It is only partially ionised, giving a lower concentration of hydrogen ions Correct answer.

Explanation

A weak acid ionises only partially in water, so fewer hydrogen ions are released than from a strong acid of the same concentration. This is why ethanoic acid has a higher pH and reacts more slowly than hydrochloric acid of equal concentration. Complete ionisation is the mark of a strong acid.

Question 14Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which pair of elements would show the most similar chemical properties?

  1. Lithium and sodium Correct answer.
  2. Lithium and beryllium
  3. Sodium and magnesium
  4. Carbon and nitrogen

Explanation

Lithium and sodium both belong to Group 1, the alkali metals, so they have the same number of outer electrons and similar chemical behaviour. Elements in different groups or periods differ in outer-shell structure and therefore in properties. This is the basis of the periodic table.

Question 15Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Why does the reactivity of Group 1 metals increase down the group?

  1. The atoms contain fewer shells of electrons
  2. The metals form covalent bonds more readily
  3. The outer electron is further from the nucleus and lost more easily Correct answer.
  4. The atoms have more protons pulling strongly on the outer electron

Explanation

Down Group 1 the atoms gain extra electron shells, so the single outer electron is further from the nucleus and shielded by inner electrons. It is therefore lost more easily, making the metal more reactive. Group 1 metals form ionic compounds by losing this electron.

Question 16Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which salt is obtained when zinc reacts with dilute nitric acid?

  1. Zinc nitrate Correct answer.
  2. Zinc nitrite
  3. Zinc oxide
  4. Zinc hydroxide

Explanation

When a metal reacts with an acid, the salt formed contains the metal cation and the anion of the acid. Nitric acid supplies nitrate ions, so zinc gives zinc nitrate and hydrogen gas. Nitrite, hydroxide and oxide are not the products of this reaction.

Question 17Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement explains why carbon forms a very large number of compounds?

  1. Carbon is a metal that forms ionic compounds easily
  2. Carbon atoms cannot bond to other carbon atoms
  3. Carbon atoms can bond to one another in chains and rings and form four bonds Correct answer.
  4. Carbon atoms can form only single bonds with other elements

Explanation

Carbon has four valence electrons, so it can form four covalent bonds, and it can bond to other carbon atoms to make chains, branches and rings. This catenation, combined with bonding to hydrogen, oxygen and nitrogen, produces millions of carbon compounds. Ionic behaviour is not the reason.

Question 18Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

In the reaction Fe + CuSO4 -> FeSO4 + Cu, which substance is oxidised?

  1. Copper sulphate
  2. Iron Correct answer.
  3. Sulphate ion
  4. Copper

Explanation

Oxidation is loss of electrons, and in this displacement reaction iron atoms lose electrons to form iron(II) ions. At the same time copper ions gain electrons and are reduced to copper metal. The sulphate ion does not change.

Question 19Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which gas is released when dilute hydrochloric acid is added to sodium carbonate?

  1. Hydrogen
  2. Carbon dioxide Correct answer.
  3. Oxygen
  4. Sulphur dioxide

Explanation

Acids react with carbonates to give a salt, water and carbon dioxide. The carbon dioxide can be confirmed because it turns limewater milky. Hydrogen would indicate a metal, and oxygen or sulphur dioxide are not produced here.

Question 20Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement about the reaction between hydrogen and chlorine to form hydrogen chloride is correct?

  1. Hydrogen chloride is a metal chloride that is insoluble in water
  2. Hydrogen chloride is an ionic solid that conducts electricity when solid
  3. Hydrogen chloride is a neutral compound that does not affect litmus
  4. Hydrogen chloride is a covalent compound that forms an acidic solution in water Correct answer.

Explanation

Hydrogen and chlorine are both non-metals, so they share electrons to form the covalent molecule HCl. When dissolved in water it ionises to give hydrogen ions, producing hydrochloric acid, which turns blue litmus red. In the pure gaseous or liquid form it does not conduct.

Question 21Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

A chloride of a metal M has the formula MCl2. What is the most likely formula of its oxide?

  1. M2O3
  2. MO Correct answer.
  3. MO2
  4. M2O

Explanation

In MCl2 the metal M balances two chloride ions, each with a charge of -1, so M has a valency of 2. Oxide ions carry a charge of -2, so one M ion combines with one oxide ion to give MO. The other formulas would not balance the charges.

Question 22Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which observation best distinguishes a strong acid from a weak acid of the same concentration?

  1. The strong acid has a higher pH and conducts electricity poorly
  2. The strong acid shows a lower pH and conducts electricity better Correct answer.
  3. Both acids show exactly the same pH and conductivity
  4. The weak acid turns litmus red while the strong acid does not

Explanation

A strong acid ionises almost completely, releasing more hydrogen ions than a weak acid of the same concentration. The greater ion concentration gives a lower pH and better electrical conductivity. Both acids would still turn blue litmus red.

Question 23Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Why does the atomic radius decrease across a period from left to right?

  1. Nuclear charge increases while electrons enter the same shell, pulling them closer Correct answer.
  2. Electrons are lost, leaving smaller ions
  3. The number of protons decreases across the period
  4. New shells are added, increasing the distance of outer electrons

Explanation

Across a period the number of protons increases, so the nuclear charge rises, while the added electrons enter the same outer shell. The stronger attraction draws the electron cloud closer, so atomic radius decreases. Adding shells happens down a group, not across a period.

Question 24Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

In the reaction between ethene and bromine water, what is observed and what type of reaction occurs?

  1. The colour deepens because bromine is oxidised
  2. A gas is evolved and the solution becomes alkaline
  3. The orange-brown colour is decolourised by an addition reaction Correct answer.
  4. No change occurs because ethene is saturated

Explanation

Ethene contains a carbon-carbon double bond, so it undergoes addition reactions. Bromine adds across the double bond, forming colourless 1,2-dibromoethane, and the orange-brown colour of bromine water disappears. This decolourisation is a standard test for unsaturation.

Question 25Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

A metal carbonate decomposes on heating to give a metal oxide and carbon dioxide. Which metal carbonate is most easily decomposed by heat?

  1. Potassium carbonate
  2. Sodium carbonate
  3. Copper carbonate Correct answer.
  4. Calcium carbonate heated only gently

Explanation

The thermal stability of metal carbonates increases with the reactivity of the metal. Carbonates of very reactive metals such as sodium and potassium are stable even at high temperatures, while those of less reactive metals such as copper decompose readily on gentle heating. Calcium carbonate needs strong heating.

Question 26Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which ion is responsible for the acidic behaviour of an aqueous solution of hydrogen chloride?

  1. Oxide ion, O²⁻
  2. Chloride ion, Cl⁻
  3. Hydrogen ion, H⁺ Correct answer.
  4. Hydroxide ion, OH⁻

Explanation

Acids produce hydrogen ions when dissolved in water, and it is these H⁺ ions that give the solution its acidic character. Hydrogen chloride ionises in water to give H⁺ and Cl⁻, but only the H⁺ is responsible for acidity. Chloride ions are the spectator anions and do not create acidic behaviour.

Question 27Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

A solution turns red litmus paper blue and has a pH of 11. Which substance could it contain?

  1. Carbon dioxide dissolved in water
  2. Hydrochloric acid
  3. Sodium hydroxide Correct answer.
  4. Sodium chloride

Explanation

A pH of 11 is basic, and bases turn red litmus blue. Sodium hydroxide is a strong base and gives a strongly basic solution. The other substances either are acidic or neutral and would not produce this pair of observations.

Question 28Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement about the reaction of dilute sulphuric acid with copper(II) oxide is correct?

  1. A white precipitate of copper hydroxide forms immediately
  2. A gas is rapidly evolved and the solid remains unchanged
  3. No reaction occurs because copper is less reactive than hydrogen
  4. A blue salt solution forms and the black solid dissolves Correct answer.

Explanation

Metal oxides are basic and react with dilute acids to form a salt and water. Copper(II) oxide is a black solid that dissolves in sulphuric acid to give blue copper(II) sulphate solution. No gas is produced in this neutralisation-type reaction.

Question 29Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which salt is formed when ammonium hydroxide solution is neutralised by dilute sulphuric acid?

  1. Ammonium sulphite
  2. Ammonium sulphide
  3. Ammonium hydrogen carbonate
  4. Ammonium sulphate Correct answer.

Explanation

Neutralisation of a base with sulphuric acid gives a sulphate salt. Ammonium hydroxide supplies the ammonium ion, so the product is ammonium sulphate. The other names involve different anions that are not present in sulphuric acid.

Question 30Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

A white crystalline salt gives a white precipitate with dilute nitric acid and silver nitrate solution. Which anion is most likely present?

  1. Sulphate
  2. Chloride Correct answer.
  3. Nitrate
  4. Carbonate

Explanation

Silver nitrate solution gives a white precipitate of silver chloride with chloride ions, and dilute nitric acid is added to remove interfering carbonate ions. Sulphate would be tested with barium chloride, and carbonate would give effervescence with acid. Nitrate gives no precipitate with silver nitrate.

Question 31Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which method is most suitable for obtaining pure copper(II) sulphate crystals from a solution containing dissolved copper(II) sulphate?

  1. Filtration through filter paper
  2. Crystallisation by slow evaporation Correct answer.
  3. Decantation of the upper layer
  4. Distillation to collect the solvent

Explanation

A dissolved salt can be recovered by crystallising it from a saturated solution through controlled evaporation. Filtration and decantation separate insoluble solids, not dissolved salts. Distillation would mainly recover water and leave impure residue.

Question 32Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which property is characteristic of metals rather than non-metals?

  1. They form acidic oxides
  2. They are brittle when solid
  3. They are poor conductors of heat
  4. They form basic oxides Correct answer.

Explanation

Metals generally form basic oxides, which react with acids to give salts and water. Non-metals typically form acidic or neutral oxides. Poor heat conduction and brittleness are properties of non-metals, not metals.

Question 33Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

A metal M is placed in dilute hydrochloric acid and no bubbles appear, but M displaces silver from silver nitrate solution. Which metal could M be?

  1. Magnesium
  2. Sodium
  3. Zinc
  4. Copper Correct answer.

Explanation

Copper lies below hydrogen in the reactivity series, so it does not liberate hydrogen from dilute acid, yet it lies above silver and so displaces silver. Magnesium, zinc and sodium all react with dilute acid to give hydrogen. This pattern fits copper alone.

Question 34Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

In the thermite reaction, aluminium powder is heated with iron(III) oxide and molten iron is produced. Which statement best explains why this reaction occurs?

  1. Aluminium oxide is soluble in molten iron
  2. Aluminium is more reactive than iron and reduces the oxide Correct answer.
  3. Iron is more reactive than aluminium and displaces it
  4. Both metals have equal reactivity so the reaction is reversible

Explanation

A more reactive metal can displace a less reactive metal from its oxide. Aluminium is higher than iron in the reactivity series, so it takes the oxygen and leaves molten iron. The large heat release makes the iron molten.

Question 35Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement explains why sodium is stored under kerosene oil?

  1. It loses its metallic lustre when exposed to light
  2. It reacts rapidly with oxygen and moisture in air Correct answer.
  3. It dissolves slowly in kerosene to form a solution
  4. It reacts with kerosene to produce a protective coating

Explanation

Sodium is a very reactive metal that reacts quickly with oxygen and water vapour in air, so it must be kept away from air. Kerosene is unreactive towards sodium and forms a barrier. Tarnishing alone would not require such storage.

Question 36Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which pair of substances reacts to produce a salt, water and a gas that turns limewater milky?

  1. Sodium chloride and dilute hydrochloric acid
  2. Sodium carbonate and dilute hydrochloric acid Correct answer.
  3. Sodium nitrate and dilute hydrochloric acid
  4. Sodium sulphate and dilute hydrochloric acid

Explanation

Carbonates react with dilute acids to give a salt, water and carbon dioxide, and carbon dioxide turns limewater milky. Chlorides, sulphates and nitrates do not release carbon dioxide with dilute acid. Only the carbonate provides the carbonate ion needed.

Question 37Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

A reaction is described as exothermic. Which change accompanies such a reaction?

  1. The surroundings become cooler as heat is absorbed
  2. No heat change occurs but a gas is always evolved
  3. The reaction stops unless the mixture is continuously heated
  4. The surroundings become warmer as heat is released Correct answer.

Explanation

In an exothermic reaction, energy is released to the surroundings, so the temperature of the surroundings rises. Endothermic reactions absorb heat and cool the surroundings. Gas evolution and heating requirements are not defining features of exothermic reactions.

Question 38Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

In the reaction Zn + 2HCl → ZnCl₂ + H₂, which species is reduced?

  1. Chlorine, because it loses electrons
  2. Hydrogen in HCl, because it gains electrons Correct answer.
  3. Zinc chloride, because it is the product
  4. Zinc, because it gains electrons

Explanation

Reduction is gain of electrons, shown as a decrease in oxidation number. Hydrogen in HCl has oxidation number +1 and becomes 0 in H₂, so it is reduced. Zinc is oxidised from 0 to +2, and chlorine keeps its oxidation number of −1.

Question 39Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which reaction is an example of a displacement reaction?

  1. Burning magnesium ribbon in air
  2. Iron nail dipped in copper(II) sulphate solution Correct answer.
  3. Adding dilute acid to sodium hydroxide
  4. Heating calcium carbonate strongly

Explanation

In a displacement reaction a more reactive element pushes a less reactive element out of its compound. Iron displaces copper from copper(II) sulphate because iron is more reactive. Burning, decomposition and neutralisation are different reaction types.

Question 40Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement about the members of a homologous series is correct?

  1. They all contain a double bond between carbon atoms
  2. They show a gradual change in physical properties with increasing chain length Correct answer.
  3. They all react in exactly the same way at the same rate
  4. They all have identical molecular formulae

Explanation

Members of a homologous series share a general formula and similar chemical properties, but physical properties such as boiling point change gradually as the chain lengthens. They differ by one CH₂ unit, so molecular formulae are not identical. Not all series contain double bonds.

Question 41Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which product is formed when ethanol is oxidised by acidified potassium dichromate solution?

  1. Ethyl ethanoate
  2. Ethene
  3. Methane
  4. Ethanoic acid Correct answer.

Explanation

Acidified potassium dichromate is a strong oxidising agent that converts ethanol first to ethanal and then to ethanoic acid. The orange dichromate turns green as it is reduced. The other products are not formed by this oxidation.

Question 42Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement explains why ethanoic acid reacts with sodium carbonate to release carbon dioxide while ethanol does not?

  1. Sodium carbonate reacts only with compounds containing oxygen
  2. Ethanoic acid contains a carboxyl group that supplies acidic hydrogen ions Correct answer.
  3. Ethanol contains more carbon atoms than ethanoic acid
  4. Ethanol is a stronger acid than ethanoic acid

Explanation

The carboxyl group of ethanoic acid releases H⁺ ions in water, and these react with carbonate to liberate carbon dioxide. Ethanol has a hydroxyl group attached to carbon and is essentially neutral, so it does not react with carbonate. The number of carbon atoms and oxygen content are not the deciding factors.

Question 43Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement about soaps and detergents is correct?

  1. Detergents cannot form micelles in water
  2. Soap molecules have a hydrocarbon tail that dissolves grease and an ionic head that dissolves in water Correct answer.
  3. Soaps work well in hard water because calcium ions help them dissolve grease
  4. Soap molecules have an ionic tail and a hydrocarbon head

Explanation

Soap molecules are amphiphilic: a long hydrocarbon tail dissolves in grease while the ionic head remains in water, forming micelles that lift grease away. Soaps form scum with calcium and magnesium ions in hard water, whereas detergents avoid this problem. Detergents also form micelles.

Question 44Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which pair of elements belongs to the same period of the modern periodic table?

  1. Sodium and potassium
  2. Magnesium and calcium
  3. Sodium and chlorine Correct answer.
  4. Chlorine and bromine

Explanation

Elements in the same period have the same number of electron shells and appear in the same horizontal row. Sodium and chlorine both lie in the third period. The other pairs are in the same group but different periods.

Question 45Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

An element has the electronic configuration 2, 8, 7. In which group and period of the periodic table does it lie?

  1. Group 7, period 2
  2. Group 17, period 3 Correct answer.
  3. Group 15, period 3
  4. Group 3, period 17

Explanation

The number of shells gives the period, so three shells place it in period 3. The number of outer electrons gives the group for main-group elements, and seven outer electrons place it in Group 17. The element is chlorine.

Question 46Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement best explains why noble gases are chemically very unreactive?

  1. They are all radioactive and decay too quickly to react
  2. They have complete outer electron shells and no tendency to gain or lose electrons Correct answer.
  3. They have very large atomic radii that prevent bonding
  4. They have only one electron in their outermost shell

Explanation

Noble gases have full outer shells, giving a stable electronic arrangement with no need to gain or lose electrons. This closed-shell configuration accounts for their very low reactivity. Atomic size and radioactivity do not explain the pattern.

Question 47Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Across period 3 from sodium to chlorine, which trend is observed?

  1. Oxides change from acidic through amphoteric to basic
  2. Metallic character increases steadily
  3. The elements become better at losing electrons
  4. Oxides change from basic through amphoteric to acidic Correct answer.

Explanation

Sodium and magnesium form basic oxides, aluminium oxide is amphoteric, and the oxides of silicon, phosphorus, sulphur and chlorine are acidic. This reflects increasing non-metallic character across the period. Metallic character and the tendency to lose electrons decrease from left to right.

Question 48Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which property generally increases down Group 1 from lithium to caesium?

  1. Atomic radius and metallic character Correct answer.
  2. Number of outer-shell electrons
  3. Non-metallic character
  4. Electronegativity and ionisation energy

Explanation

Each step down Group 1 adds a shell, so atomic radius increases and the outer electron is lost more easily, increasing metallic character. Electronegativity and ionisation energy decrease down the group. The number of outer electrons stays at one.

Question 49Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

An element X forms a chloride with the formula XCl₃ and its oxide is amphoteric. Which element is most likely to be X?

  1. Sodium
  2. Sulphur
  3. Magnesium
  4. Aluminium Correct answer.

Explanation

Aluminium forms AlCl₃ and has an amphoteric oxide, Al₂O₃, which reacts with both acids and alkalis. Sodium and magnesium form basic oxides with formulae NaCl and MgCl₂. Sulphur forms an acidic oxide and a chloride with a different formula.

Question 50Chemical Substances: Nature and Behaviour (chemical reactions, acids/bases/salts, metals and non-metals, carbon compounds, periodic classification)

Which statement about the modern periodic table arrangement is correct?

  1. Elements are arranged in order of increasing atomic number Correct answer.
  2. Elements are grouped strictly by physical state at room temperature
  3. Elements are arranged in order of increasing atomic mass only
  4. Elements are arranged alphabetically by symbol

Explanation

The modern periodic table orders elements by increasing atomic number, which is the number of protons in the nucleus. This resolves anomalies that arose in earlier mass-based arrangements. Physical state and alphabetical order play no part in the arrangement.