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Bihar BSEB Matric Science study materials
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Bihar BSEB Matric Science practice questions

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Question 1Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

The equation Fe + H2O → Fe3O4 + H2 is to be balanced. Which set of coefficients, written in the order Fe, H2O, Fe3O4, H2, balances it correctly?

  1. 3, 4, 1, 4 Correct answer.
  2. 3, 4, 1, 2
  3. 2, 3, 1, 3
  4. 1, 4, 1, 4

Explanation

Balancing means the number of atoms of each element must be equal on both sides, as required by the law of conservation of mass. With 3 Fe, 4 H2O, 1 Fe3O4 and 4 H2, both sides contain 3 iron atoms, 8 hydrogen atoms and 4 oxygen atoms.

Question 2Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

A sample of lemon juice has a pH of about 2. Which statement correctly describes this juice?

  1. It is acidic and turns red litmus blue.
  2. It is neutral and does not change litmus.
  3. It is basic and turns red litmus blue.
  4. It is acidic and turns blue litmus red. Correct answer.

Explanation

The pH scale runs from 0 to 14, with values below 7 showing acidity and values above 7 showing basicity. A pH of 2 is clearly acidic, and acids change blue litmus paper to red.

Question 3Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Four metals are placed in separate beakers of cold water. Which of them reacts most vigorously, being highest in the reactivity series?

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

Explanation

In the reactivity series the order is sodium, then zinc, then iron, then copper. Sodium loses electrons most readily and reacts vigorously with cold water to give sodium hydroxide and hydrogen, so it is the most reactive of these four metals.

Question 4Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Lead(II) nitrate is heated strongly in a dry test tube and brown fumes along with another colourless gas are released. Which pair of gases is formed?

  1. Brown nitric oxide gas together with oxygen gas
  2. Brown nitrogen dioxide gas with oxygen gas Correct answer.
  3. Colourless nitrogen dioxide gas with hydrogen gas
  4. Brown sulphur dioxide gas together with oxygen gas

Explanation

On strong heating, lead(II) nitrate undergoes thermal decomposition: 2Pb(NO3)2 → 2PbO + 4NO2 + O2. The brown fumes are nitrogen dioxide and the colourless gas is oxygen, which relights a glowing splint.

Question 5Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Zinc granules are added to dilute sulphuric acid in a test tube. Which observation and equation are both correct?

  1. A colourless gas burns with a pop; Zn + H2SO4 → ZnSO4 + H2 Correct answer.
  2. A colourless gas turns limewater milky; Zn + H2SO4 → ZnSO3 + H2O
  3. No reaction occurs; zinc is less reactive than hydrogen
  4. A green gas bleaches litmus; Zn + H2SO4 → ZnS + H2O

Explanation

Zinc lies above hydrogen in the reactivity series, so it displaces hydrogen from dilute sulphuric acid and forms zinc sulphate: Zn + H2SO4 → ZnSO4 + H2. The hydrogen collected burns with a pop when a burning splint is brought near it.

Question 6Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Packets of fried potato chips are flushed with nitrogen gas before sealing. What is the purpose of this?

  1. To supply nitrogen as an extra nutrient to the food
  2. To kill bacteria by making the inside of the packet acidic
  3. To keep the chips moist and soft for a longer time
  4. To stop fats and oils being oxidised and turning rancid Correct answer.

Explanation

Fats and oils in fried foods react with oxygen and turn rancid, developing an unpleasant smell and taste. Nitrogen is chemically unreactive, so flushing the packet with it displaces oxygen and slows down this oxidation.

Question 7Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Aluminium oxide reacts with dilute hydrochloric acid to give aluminium chloride, and it also reacts with sodium hydroxide solution to give sodium aluminate. What does this behaviour show about aluminium oxide?

  1. It is a neutral oxide, like carbon monoxide.
  2. It is an acidic oxide only, like carbon dioxide.
  3. It is a basic oxide only, like magnesium oxide.
  4. It is amphoteric in nature. Correct answer.

Explanation

An oxide that reacts with both acids and bases to form salts is described as amphoteric. Aluminium oxide shows this dual behaviour, reacting with hydrochloric acid as a base and with sodium hydroxide as an acid.

Question 8Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

A clean iron nail is kept dipped in copper sulphate solution for about twenty minutes. Which change is observed?

  1. The solution turns deep blue and a grey deposit forms on the nail.
  2. No change is seen because iron is less reactive than copper.
  3. A reddish-brown deposit forms and the solution stays blue.
  4. A reddish-brown deposit forms and the blue colour of the solution fades. Correct answer.

Explanation

Iron lies above copper in the reactivity series and displaces it: Fe + CuSO4 → FeSO4 + Cu. Copper is deposited as a reddish-brown coating on the nail, while the blue colour fades as copper ions leave the solution and pale green iron(II) sulphate forms.

Question 9Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

In the reaction CuO + H2 → Cu + H2O, which statement about the reactants is correct?

  1. Copper(II) oxide is oxidised and acts as the reducing agent.
  2. Copper(II) oxide is reduced and acts as the oxidising agent. Correct answer.
  3. Hydrogen is reduced and acts as the oxidising agent.
  4. Neither reactant changes, because no free oxygen gas is involved.

Explanation

Copper(II) oxide loses oxygen and is therefore reduced, and the substance that is reduced acts as the oxidising agent. Hydrogen gains that oxygen and is oxidised, so it acts as the reducing agent in this reaction.

Question 10Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Solid sodium chloride does not conduct electricity, but its aqueous solution does. What is the correct explanation?

  1. Water reacts with sodium chloride and releases free electrons that carry the current.
  2. Solid sodium chloride is a covalent compound and therefore contains no charged particles.
  3. Solid sodium chloride contains no charged particles at all; ions are produced only when it dissolves.
  4. In solution the ions are free to move, while in the solid they are held in fixed positions in the lattice. Correct answer.

Explanation

Sodium chloride is an ionic compound built from Na+ and Cl- ions. In the solid state these ions are locked in a rigid lattice and cannot move, but on dissolving or melting they become mobile and can carry electric current.

Question 11Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Which of the following changes is an example of a combination reaction?

  1. Sodium hydroxide solution neutralising dilute hydrochloric acid
  2. Zinc displacing copper from copper sulphate solution
  3. Calcium carbonate breaking into calcium oxide and carbon dioxide on strong heating
  4. Calcium oxide reacting with water to form calcium hydroxide Correct answer.

Explanation

In a combination reaction two or more reactants join to form a single product, as in CaO + H2O → Ca(OH)2. The heating of limestone is a decomposition reaction, the zinc case is a displacement reaction, and acid-base neutralisation is a double displacement reaction.

Question 12Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Which of the following liquids has a pH greater than 7?

  1. Vinegar
  2. Pure water
  3. Dilute hydrochloric acid
  4. Sodium hydroxide solution Correct answer.

Explanation

The pH scale runs from 0 to 14, with values above 7 showing basic (alkaline) character. Sodium hydroxide is a strong base, so its solution has a pH of about 13–14, while acids such as hydrochloric acid and vinegar lie below 7 and pure water is exactly 7 at 25 °C.

Question 13Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Brass, used for making utensils and decorative articles, is an alloy of which pair of metals?

  1. Lead and tin
  2. Iron and carbon
  3. Copper and zinc Correct answer.
  4. Copper and tin

Explanation

Brass is made by mixing copper with zinc, which makes the material harder and more corrosion resistant than pure copper. Copper with tin gives bronze, iron with carbon gives steel, and lead with tin gives solder.

Question 14Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Dilute hydrochloric acid is added drop by drop to sodium carbonate taken in a test tube. Which observation with the correct balanced equation matches this reaction?

  1. No gas is produced; Na2CO3 + 2HCl → 2NaCl + H2O
  2. A gas with a pungent choking smell is produced; Na2CO3 + 2HCl → 2NaCl + H2O + SO2
  3. A gas that burns with a pop is produced; Na2CO3 + 2HCl → 2NaCl + H2O + H2
  4. Brisk effervescence of a gas that turns lime water milky; Na2CO3 + 2HCl → 2NaCl + H2O + CO2 Correct answer.

Explanation

A metal carbonate reacts with a dilute acid to give a salt, water and carbon dioxide, which is the gas that turns lime water milky. In the balanced equation two HCl molecules supply the two chloride ions and two hydrogen atoms needed, so the coefficients 2, 2 and 2 must be used.

Question 15Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Copper does not liberate hydrogen gas when kept in dilute hydrochloric acid. What is the reason?

  1. Copper has a protective coating that blocks every acid
  2. Copper reacts with acids only when they are concentrated and hot
  3. Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen Correct answer.
  4. Copper is a non-metal and therefore does not react with any acid

Explanation

Only metals placed above hydrogen in the reactivity series can displace hydrogen ions from a dilute acid. Copper lies below hydrogen, so it has no tendency to lose electrons to H⁺ ions and no hydrogen gas is seen.

Question 16Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Solutions of hydrochloric acid and acetic acid of the same concentration are tested with pH paper. Which statement is correct?

  1. Both acids ionise completely, so both solutions give the same pH
  2. Hydrochloric acid gives the lower pH because it ionises completely in water Correct answer.
  3. Neither solution conducts electricity because both acids are covalent compounds
  4. Acetic acid gives the lower pH because its molecule has more hydrogen atoms

Explanation

Hydrochloric acid is a strong acid and dissociates almost completely, so it gives a high concentration of hydrogen ions and a low pH. Acetic acid is a weak acid that ionises only partly, giving fewer hydrogen ions and a higher pH at the same concentration.

Question 17Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

A person with an acidic stomach is given a spoon of milk of magnesia. What is the role of this medicine?

  1. It is a base that neutralises the excess hydrochloric acid in the stomach Correct answer.
  2. It is a salt that stops the stomach from producing any more acid
  3. It is an acid that increases the acidity to help digestion
  4. It is an indicator that shows the pH inside the stomach

Explanation

Milk of magnesia is a suspension of magnesium hydroxide, a mild base that neutralises excess hydrochloric acid in the stomach to give magnesium chloride and water. This removes the burning sensation without making the stomach contents strongly basic.

Question 18Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Sodium chloride melts at about 801 °C, while iodine melts at about 114 °C. Why does sodium chloride need such a high temperature to melt?

  1. Its molecules are held together only by weak forces of attraction
  2. It has covalent bonds between sodium atoms and chlorine atoms
  3. It has a giant molecular network held by strong covalent bonds
  4. Strong electrostatic forces between oppositely charged ions must be overcome Correct answer.

Explanation

Sodium chloride is an ionic solid built from a three-dimensional lattice of Na⁺ and Cl⁻ ions held by strong electrostatic attraction. Melting requires enough energy to break this lattice, so the melting point is high, whereas iodine is molecular with only weak forces between molecules.

Question 19Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

In the reaction Fe2O3 + 2Al → 2Fe + Al2O3, a large amount of heat is released and the molten iron is used to join broken railway tracks. Which statement about this reaction is correct?

  1. The change is a combination reaction as two reactants give two products
  2. Iron(III) oxide is oxidised to iron metal during this reaction
  3. Aluminium is reduced, and iron(III) oxide acts as the reducing agent
  4. Aluminium is the reducing agent because it is more reactive than iron Correct answer.

Explanation

Aluminium lies above iron in the reactivity series, so it takes oxygen away from iron(III) oxide and is itself oxidised to Al2O3. The substance that removes oxygen is the reducing agent, and here it is aluminium, while iron(III) oxide is reduced to iron.

Question 20Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Iron sheets are coated with zinc (galvanisation). Even when the coating is scratched and bare iron is exposed, rusting does not spread from the damaged area. Why?

  1. Zinc changes the surface of the iron into an alloy that cannot rust
  2. Zinc is more reactive than iron, so zinc is oxidised in preference to iron Correct answer.
  3. Zinc is less reactive than iron, so it stays unchanged and covers the iron
  4. Zinc forms a hard oxide plug that seals the scratch, so no metal reacts there

Explanation

Zinc is placed above iron in the reactivity series, so it loses electrons more readily and is corroded first, a behaviour called sacrificial protection. As long as some zinc remains near the exposed iron, the iron is protected even though the coating is broken.

Question 21Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Which of the following changes is an example of a decomposition reaction?

  1. Burning magnesium ribbon in air to form magnesium oxide
  2. Dipping an iron nail in copper sulphate solution to deposit copper
  3. Heating calcium carbonate strongly to give calcium oxide and carbon dioxide Correct answer.
  4. Adding zinc granules to dilute sulphuric acid to form zinc sulphate and hydrogen

Explanation

A decomposition reaction is one in which a single compound breaks down into two or more simpler substances, usually on heating, exposure to light, or passing electricity. Heating calcium carbonate gives calcium oxide and carbon dioxide, so one reactant forms two products. The other changes are combination or displacement reactions.

Question 22Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

A colourless solution turns red litmus paper blue. What is the nature of the solution?

  1. Acidic
  2. Strongly acidic
  3. Basic Correct answer.
  4. Neutral

Explanation

Litmus is an acid-base indicator: acids turn blue litmus red, while bases turn red litmus blue. Since the solution changes red litmus to blue, it must be basic. A neutral solution causes no change in litmus colour.

Question 23Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Which non-metal is a shiny, purple-black solid that sublimes on heating and is used as an antiseptic?

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

Explanation

Most non-metals are dull, but iodine is an exception: it is a shiny, purple-black solid that sublimes to a violet vapour. It is also used as a mild antiseptic. Sulphur is yellow, phosphorus is waxy, and carbon is generally black.

Question 24Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Aluminium burns in oxygen to form aluminium oxide: Al + O2 → Al2O3. Which set of coefficients balances the equation in the order Al, O2, Al2O3?

  1. 2, 1, 2
  2. 3, 2, 1
  3. 4, 3, 2 Correct answer.
  4. 2, 3, 1

Explanation

The balanced equation is 4Al + 3O2 → 2Al2O3. Four aluminium atoms on the left match four aluminium atoms in two Al2O3 units, and six oxygen atoms on the left match six oxygen atoms on the right. Balancing requires equal numbers of each kind of atom on both sides.

Question 25Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

A bee sting causes pain because it injects an acid. Which common household substance is most suitable to rub on the sting for relief?

  1. Common salt solution
  2. Vinegar
  3. Lemon juice
  4. Baking soda paste Correct answer.

Explanation

Baking soda is a mild base, so it neutralises the acid injected by the bee and reduces the pain. Vinegar and lemon juice are themselves acidic and would increase the acidity instead of relieving it. A salt solution is neutral and does not neutralise the acid effectively.

Question 26Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Why is sodium metal stored under kerosene oil?

  1. To make it soft and easy to cut
  2. To prevent it from reacting with oxygen and moisture in the air Correct answer.
  3. To increase its reactivity with water
  4. To dissolve the oxide layer formed on it

Explanation

Sodium is a very reactive metal that reacts rapidly with oxygen and moisture in air, so it cannot be kept in the open. Kerosene oil keeps air and moisture away from the metal and prevents this reaction. It does not soften sodium or increase its reactivity.

Question 27Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Which pair contains a strong acid and a weak base?

  1. Nitric acid and potassium hydroxide solution
  2. Hydrochloric acid and sodium hydroxide solution
  3. Acetic acid and ammonium hydroxide solution
  4. Sulphuric acid and ammonium hydroxide Correct answer.

Explanation

Sulphuric acid is a strong acid because it ionises almost completely in water, while ammonium hydroxide is a weak base because it ionises only partially. Hydrochloric acid with sodium hydroxide and nitric acid with potassium hydroxide are pairs of strong acids with strong bases. Acetic acid with ammonium hydroxide is a weak acid with a weak base.

Question 28Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

On heating blue copper sulphate crystals, they turn white. What is the correct explanation for this change?

  1. Copper sulphate decomposes into copper and sulphur
  2. Copper sulphate is oxidised to copper oxide
  3. Copper sulphate loses its water of crystallisation Correct answer.
  4. Copper sulphate is reduced to copper metal

Explanation

Blue copper sulphate crystals contain five molecules of water of crystallisation per formula unit, written as CuSO4·5H2O. On heating, this water is lost and white anhydrous copper sulphate is left. Adding water to the white solid restores the blue colour, showing that the change is due to loss of water.

Question 29Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

In the reaction MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O, which substance is oxidised?

  1. HCl Correct answer.
  2. MnO2
  3. MnCl2
  4. H2O

Explanation

Oxidation involves loss of electrons or an increase in oxidation number. In HCl, chlorine has an oxidation number of -1, and in Cl2 it is 0, so chloride ions from HCl are oxidised to chlorine gas. Manganese in MnO2 is reduced from +4 to +2 in MnCl2.

Question 30Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

An aqueous solution of sodium acetate is basic. Which statement explains this?

  1. Acetate ions hydrolyse with water to produce hydrogen ions
  2. Sodium acetate does not dissociate in water
  3. Sodium ions react with water to produce hydroxide ions
  4. Acetate ions hydrolyse with water to produce hydroxide ions Correct answer.

Explanation

Sodium acetate is a salt of a strong base, sodium hydroxide, and a weak acid, acetic acid. In water, the acetate ion hydrolyses by accepting a hydrogen ion from water, leaving an excess of hydroxide ions and making the solution basic. Sodium ions do not hydrolyse in water.

Question 31Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Zinc granules are added to dilute sulphuric acid taken in a test tube and a gas is collected at the mouth of the tube. Which gas is evolved in this reaction?

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

Explanation

Dilute acids react with metals such as zinc, magnesium and iron to give a salt and hydrogen gas; here zinc sulphate and hydrogen are formed. When a burning splint is brought near the gas it burns with a pop sound, which is the standard identification test for hydrogen.

Question 32Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Baking soda, used in making cakes and in antacid tablets, is known by which chemical name?

  1. Sodium hydrogencarbonate Correct answer.
  2. Sodium carbonate
  3. Calcium sulphate
  4. Sodium chloride

Explanation

Baking soda is sodium hydrogencarbonate, NaHCO3, a mild base that gives off carbon dioxide with acids and is therefore used in antacids and baking powder. Sodium carbonate is washing soda, and sodium chloride is common salt, so neither of them is baking soda.

Question 33Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Silver nitrate solution is mixed with sodium chloride solution and a white precipitate is produced. Which type of reaction is this, and what is the precipitate?

  1. Double displacement reaction, silver chloride Correct answer.
  2. Displacement reaction, silver metal
  3. Combination reaction, sodium nitrate
  4. Decomposition reaction, silver chloride

Explanation

The two salt solutions exchange ions: silver ions combine with chloride ions to form insoluble silver chloride, which appears as a white precipitate, while sodium nitrate remains dissolved. Because the exchange of ions produces a precipitate, the reaction is a double displacement (precipitation) reaction.

Question 34Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Which pair of oxides reacts with dilute hydrochloric acid as well as with sodium hydroxide solution, that is, which pair is amphoteric?

  1. Sodium oxide and potassium oxide
  2. Carbon dioxide and sulphur dioxide
  3. Aluminium oxide and zinc oxide Correct answer.
  4. Calcium oxide and magnesium oxide

Explanation

Amphoteric oxides react with acids to form a salt and water and also with bases to form a salt and water; aluminium oxide and zinc oxide behave in exactly this way. Sodium, potassium, calcium and magnesium oxides are basic and react only with acids, while carbon dioxide and sulphur dioxide are acidic and react only with bases.

Question 35Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

A few drops of phenolphthalein are added to dilute sodium hydroxide solution and dilute hydrochloric acid is then added drop by drop until the solution becomes acidic. What colour changes are seen?

  1. Yellow, then orange
  2. Pink, then colourless Correct answer.
  3. Colourless, then pink
  4. Blue, then red

Explanation

Phenolphthalein is pink in basic solutions but colourless in neutral and acidic solutions. Sodium hydroxide solution makes it pink; as hydrochloric acid neutralises the alkali and an excess makes the mixture acidic, the pink colour fades and finally disappears.

Question 36Chemical Reactions and Equations, Acids-Bases-Salts, Metals and Non-metals

Three metals X, Y and Z are tested with salt solutions. X displaces Y from a solution of a Y salt but cannot displace Z; Y also cannot displace Z. Which order of reactivity fits these observations?

  1. Y > X > Z
  2. X > Y > Z
  3. X > Z > Y
  4. Z > X > Y Correct answer.

Explanation

A more reactive metal displaces a less reactive metal from its salt solution. X displaces Y, so X is above Y; X cannot displace Z and Y cannot displace Z, so Z must lie above both X and Y. The reactivity order is therefore Z > X > Y.

Question 37Carbon and its Compounds; Periodic Classification of Elements

Carbon forms four covalent bonds in most of its compounds by sharing four pairs of electrons. This property of carbon is known as:

  1. Tetravalency Correct answer.
  2. Catenation
  3. Isomerism
  4. Allotropy

Explanation

A carbon atom has four electrons in its outermost shell, so it needs four more to complete an octet and therefore forms four covalent bonds, as in methane and carbon dioxide. This ability is called tetravalency. The other three terms describe self-linkage of carbon atoms, existence of an element in different physical forms, and compounds having the same molecular formula but different structures.

Question 38Carbon and its Compounds; Periodic Classification of Elements

Which allotrope of carbon is a good conductor of electricity and is therefore used as an electrode in dry cells?

  1. Charcoal
  2. Graphite Correct answer.
  3. Fullerene
  4. Diamond

Explanation

In graphite each carbon atom is bonded to only three neighbouring carbon atoms in flat hexagonal layers, so the fourth valence electron remains free and delocalised over the layer. These mobile electrons carry current, which makes graphite a good conductor used in electrodes and dry cells. Diamond has all four valence electrons locked in rigid sigma bonds, and charcoal and fullerene do not provide such an extended layer of free electrons.

Question 39Carbon and its Compounds; Periodic Classification of Elements

According to the modern periodic law, the properties of elements are a periodic function of their:

  1. atomic mass
  2. atomic volume
  3. number of neutrons
  4. atomic number Correct answer.

Explanation

The modern periodic table arranges elements in order of increasing atomic number, which is equal to the number of protons in the nucleus. Since chemical properties are decided by the electronic configuration, and this configuration repeats after certain intervals, properties repeat periodically. Mendeleev had used atomic mass, but that could not give isotopes a proper place or explain certain misplaced pairs such as argon and potassium.

Question 40Carbon and its Compounds; Periodic Classification of Elements

Two consecutive members of a homologous series differ in their molecular formula by one unit of:

  1. -CH2- and 14 u Correct answer.
  2. -CH3 and 15 u
  3. -C2H4- and 28 u
  4. -H and 1 u

Explanation

Members of a homologous series have the same general formula and the same functional group but differ by one -CH2- unit. Since carbon is 12 u and hydrogen is 1 u, the mass difference between successive members is 14 u. This regular step makes physical properties change gradually along the series while the chemical behaviour remains similar.

Question 41Carbon and its Compounds; Periodic Classification of Elements

A compound has the molecular formula CH3COOH. The functional group present in this compound is:

  1. -CHO, aldehyde
  2. -CO-, ketone
  3. -COOH, carboxyl Correct answer.
  4. -OH, hydroxyl

Explanation

Ethanoic acid contains the carboxyl group -COOH, in which a carbonyl carbon is attached to both a hydroxyl group and a hydrogen atom. Compounds containing this group are carboxylic acids, which turn blue litmus red and release carbon dioxide from sodium hydrogen carbonate. A hydroxyl group alone would give an alcohol and a -CHO group would give an aldehyde, so the complete carboxyl group must be identified.

Question 42Carbon and its Compounds; Periodic Classification of Elements

How many structural isomers are possible for the molecular formula C4H10?

  1. Three
  2. Two Correct answer.
  3. Four
  4. One

Explanation

C4H10 can be written as a straight chain, CH3–CH2–CH2–CH3, which is butane, or as a branched chain with a central carbon attached to three methyl groups, which is 2-methylpropane. Both have the same molecular formula but different structures, so exactly two structural isomers exist. Reading the straight chain from either end gives the same compound, so no further distinct isomer arises.

Question 43Carbon and its Compounds; Periodic Classification of Elements

Ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid. The main organic product formed is:

  1. sodium ethanoate
  2. ethyl ethanoate together with water Correct answer.
  3. ethene together with hydrogen
  4. ethanal only

Explanation

A carboxylic acid reacts with an alcohol in the presence of an acid catalyst to form an ester and water; this reaction is called esterification. Here ethanoic acid and ethanol give ethyl ethanoate, a sweet-smelling ester, with concentrated sulphuric acid acting as catalyst and dehydrating agent. Sodium ethanoate would require a base such as sodium hydroxide, and ethene is obtained by dehydrating ethanol alone.

Question 44Carbon and its Compounds; Periodic Classification of Elements

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

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

Explanation

The period is given by the number of occupied shells, and the configuration 2, 8, 7 shows three shells, so the element lies in period 3. The group is fixed by the valence electrons: seven valence electrons mean the atom is one electron short of an octet, which places it in group 17 with the halogens. Group 1 elements have a single valence electron and group 15 elements have five.

Question 45Carbon and its Compounds; Periodic Classification of Elements

Which limitation of Mendeleev's periodic table was removed only when elements were arranged by atomic number instead of atomic mass?

  1. Noble gases were unknown then
  2. It had no periods or groups
  3. Isotopes had no definite place in it Correct answer.
  4. Hydrogen did not fit any group

Explanation

Mendeleev arranged elements by increasing atomic mass, so isotopes of the same element, having different masses but identical chemical behaviour, could not be given one definite position. Some pairs such as cobalt and nickel and argon and potassium also had to be placed against the mass order to keep similar elements together. Using atomic number, which is the same for all isotopes of an element, gave every element a single definite place in the table.

Question 46Carbon and its Compounds; Periodic Classification of Elements

Moving from left to right across a period, the atomic radius of elements decreases. The correct reason for this is that:

  1. nuclear charge rises, electrons enter the same shell Correct answer.
  2. nuclear charge falls as new shells are added
  3. shells increase but nuclear charge stays the same
  4. neutrons increase and pull the outer electrons in

Explanation

Across a period, electrons are added to the same outermost shell while the number of protons in the nucleus, and hence the nuclear charge, increases steadily. The greater effective nuclear charge pulls the same shell inward more strongly, so the atomic radius decreases from left to right. Moving down a group the opposite happens, because fresh shells are added and the radius increases despite a larger nuclear charge.

Question 47Carbon and its Compounds; Periodic Classification of Elements

The ability of carbon atoms to link with one another to form long chains, branched chains and rings is called

  1. allotropy
  2. catenation Correct answer.
  3. isomerism
  4. tetravalency

Explanation

Catenation is the self-linking of carbon atoms, producing chains, branched chains and rings such as those found in alkanes and cycloalkanes. Tetravalency refers only to carbon forming four bonds, while allotropy and isomerism describe different phenomena.

Question 48Carbon and its Compounds; Periodic Classification of Elements

In the modern periodic table, the vertical columns are called ______ and the horizontal rows are called ______.

  1. groups; periods Correct answer.
  2. groups; shells
  3. periods; blocks
  4. periods; groups

Explanation

The modern periodic table has 18 vertical columns called groups and 7 horizontal rows called periods. Elements in a group have similar valence-shell configurations, while a period corresponds to the filling of a principal shell.

Question 49Carbon and its Compounds; Periodic Classification of Elements

Which functional group is characteristic of aldehydes?

  1. –COOH
  2. –CHO Correct answer.
  3. –CO–
  4. –OH

Explanation

The aldehyde functional group is –CHO, in which a carbonyl carbon is bonded to at least one hydrogen atom. Ethanal, CH3CHO, is a simple aldehyde, and Tollens' reagent can be used to detect this group.

Question 50Carbon and its Compounds; Periodic Classification of Elements

When ethene is shaken with bromine water, the orange-brown colour disappears because ethene undergoes

  1. a neutralisation reaction
  2. an addition reaction Correct answer.
  3. a displacement reaction
  4. a substitution reaction

Explanation

Ethene contains a carbon–carbon double bond, so bromine adds across the double bond to form 1,2-dibromoethane and the bromine colour fades. This addition reaction is a standard test for unsaturation.