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RBSE VU General Science study materials
RBSE VU General Science study resources

RBSE VU General Science practice questions

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Question 1Matter and Its Nature: States, Classification, and Separation

Which statement correctly describes the arrangement of particles in a solid at room temperature?

  1. Particles are closely packed but slide freely past one another.
  2. Particles are far apart and move randomly at high speed.
  3. Particles are closely packed in fixed positions and vibrate about those positions. Correct answer.
  4. Particles are far apart and arranged in a regular lattice.

Explanation

In a solid the particles are held close together by strong attractive forces and occupy fixed mean positions; they can only vibrate about these positions. This fixed arrangement gives solids a definite shape and volume. Free sliding describes liquids, and widely spaced random motion describes gases.

Question 2Matter and Its Nature: States, Classification, and Separation

A gas is transferred from a small cylinder into a much larger rigid container at the same temperature. Which property of the gas changes?

  1. The volume it occupies increases while its mass stays the same. Correct answer.
  2. Its mass decreases because the particles spread out.
  3. Both its mass and its volume stay exactly the same.
  4. Its mass increases because more space is available.

Explanation

Mass is the amount of matter and is conserved when a gas is moved between containers. Because gas particles move freely and fill any container, the volume occupied becomes that of the larger container. Therefore volume increases while mass remains unchanged.

Question 3Matter and Its Nature: States, Classification, and Separation

Which change of state involves particles gaining energy and moving from a fixed arrangement into a freely flowing arrangement?

  1. Freezing
  2. Deposition
  3. Condensation
  4. Melting Correct answer.

Explanation

Melting is the change from solid to liquid, in which particles absorb energy, break free of fixed lattice positions and become able to slide past one another. Freezing and condensation both release energy as particles become more ordered, and deposition goes directly from gas to solid.

Question 4Matter and Its Nature: States, Classification, and Separation

Sublimation is best illustrated by which observation?

  1. Ice melting into water when left in a warm room.
  2. Solid carbon dioxide forming a vapour without first becoming liquid. Correct answer.
  3. Steam condensing on a cold window pane.
  4. Salt dissolving in water to form a clear solution.

Explanation

Sublimation is the direct change from solid to vapour without passing through the liquid state. Dry ice (solid carbon dioxide) is a classic example, producing a vapour at ordinary pressure. Melting and condensation are ordinary changes of state, and dissolving is not a change of state.

Question 5Matter and Its Nature: States, Classification, and Separation

Which of the following is a homogeneous mixture?

  1. A sample of clean air from a single location Correct answer.
  2. A mixture of iron filings and sulfur powder
  3. A suspension of chalk powder in water
  4. A glass of water with visible ice cubes floating in it

Explanation

A homogeneous mixture has a uniform composition throughout, and clean air is a uniform mixture of gases. Ice cubes in water, iron filings with sulfur, and chalk in water all show visible separate parts or phases, making them heterogeneous.

Question 6Matter and Its Nature: States, Classification, and Separation

Which property is characteristic of a compound rather than of a mixture?

  1. Its composition can be varied within wide limits.
  2. Its components are present in a fixed ratio by mass. Correct answer.
  3. Its components keep their individual properties.
  4. Its components can be separated by filtration.

Explanation

A compound is formed when elements combine chemically in a definite fixed ratio by mass, and its properties differ from those of its constituent elements. Mixtures have variable composition, and their components retain their own properties and can often be separated by physical methods.

Question 7Matter and Its Nature: States, Classification, and Separation

A student separates a mixture of sand and water using a filter funnel and filter paper. Which statement explains the separation?

  1. Water evaporates completely during filtration.
  2. Sand particles are attracted to the filter paper by magnetism.
  3. Sand dissolves in water and is left behind when the water passes through.
  4. Sand particles are too large to pass through the pores of the filter paper. Correct answer.

Explanation

Filtration separates an insoluble solid from a liquid because the solid particles are larger than the pores of the filter paper, while the liquid passes through as the filtrate. Sand is insoluble in water, so it is trapped as a residue. Evaporation and magnetism play no part in this separation.

Question 8Matter and Its Nature: States, Classification, and Separation

A beaker of water contains both dissolved salt and suspended sand. Which sequence of techniques best separates all three components?

  1. Sedimentation first, then simple distillation of the sand
  2. Filtration first, then evaporation of the filtrate Correct answer.
  3. Magnetic separation first, then filtration
  4. Evaporation first, then filtration of the residue

Explanation

Filtration removes the insoluble sand as residue while salt solution passes through as filtrate. Evaporating the filtrate then leaves the dissolved salt as a solid, giving all three components separately. The other sequences either remove the wrong component first or apply an unsuitable method.

Question 9Matter and Its Nature: States, Classification, and Separation

Which method is most suitable for obtaining pure water from a solution of copper(II) sulfate in water?

  1. Magnetic separation
  2. Simple distillation Correct answer.
  3. Filtration
  4. Decantation

Explanation

Simple distillation evaporates the water and condenses the vapour in a separate vessel, leaving the dissolved copper(II) sulfate behind. This gives pure water as the distillate. Filtration, magnetic separation and decantation cannot separate a dissolved solute from its solvent.

Question 10Matter and Its Nature: States, Classification, and Separation

A liquid mixture of two miscible liquids with boiling points of 78 °C and 110 °C is to be separated. Which technique is appropriate?

  1. Paper chromatography
  2. Filtration under reduced pressure
  3. Fractional distillation Correct answer.
  4. Centrifugation

Explanation

Miscible liquids with sufficiently different boiling points are separated by fractional distillation, in which the more volatile component distils first and is condensed. Filtration removes insoluble solids, centrifugation separates suspended particles, and chromatography is used mainly for separating small amounts of dissolved substances.

Question 11Matter and Its Nature: States, Classification, and Separation

In paper chromatography of ink, the solvent front moves 8.0 cm from the origin while a blue dye moves 6.0 cm. What is the Rf value of the blue dye?

  1. 0.75 Correct answer.
  2. 0.25
  3. 6.8
  4. 1.33

Explanation

The Rf value is the distance travelled by the substance divided by the distance travelled by the solvent front, measured from the same origin. Here Rf = 6.0 cm ÷ 8.0 cm = 0.75, a dimensionless number always less than one. The other values come from inverting the ratio or subtracting the distances.

Question 12Matter and Its Nature: States, Classification, and Separation

Which observation best distinguishes a chemical change from a physical change?

  1. The substance changes from solid to liquid.
  2. The substance becomes warmer when stirred.
  3. The substance is broken into smaller pieces.
  4. A new substance with different properties is formed. Correct answer.

Explanation

A chemical change produces one or more new substances whose properties differ from those of the starting materials. Changes of state, warming during stirring and breaking into smaller pieces alter only the physical form or energy, not the chemical identity.

Question 13Matter and Its Nature: States, Classification, and Separation

When a candle burns, which statement is correct?

  1. Melting of wax is a chemical change while burning is a physical change.
  2. Melting of wax is a physical change while burning of the vapour is a chemical change. Correct answer.
  3. Both melting and burning of wax are chemical changes.
  4. Both melting and burning of wax are physical changes.

Explanation

Melting wax is only a change of state, so it is physical and the wax can be solidified again. The vapour burning in air forms new substances such as carbon dioxide and water, so combustion is chemical. The two processes occurring together must be classified separately.

Question 14Matter and Its Nature: States, Classification, and Separation

A sealed flask contains ice and water at 0 °C. Heat is supplied slowly until all the ice just melts while the temperature stays at 0 °C. What happens to the energy supplied?

  1. It raises the kinetic energy of the particles so the temperature must rise.
  2. It is lost because the flask is sealed and cannot absorb heat.
  3. It is used to overcome the forces holding particles in the solid lattice, not to raise temperature. Correct answer.
  4. It is converted into extra mass of the water.

Explanation

During melting the supplied energy is latent heat used to break the attractive forces that hold particles in the solid lattice. The average kinetic energy of the particles does not increase, so the temperature remains constant at the melting point until all the ice has melted.

Question 15Matter and Its Nature: States, Classification, and Separation

Which statement about the effect of pressure on the boiling point of a liquid is correct?

  1. External pressure has no effect on the boiling point.
  2. Increasing the external pressure raises the boiling point. Correct answer.
  3. Increasing the external pressure lowers the boiling point.
  4. Boiling point depends only on the volume of liquid present.

Explanation

A liquid boils when its vapour pressure equals the external pressure. Raising the external pressure means the liquid must be heated to a higher temperature for its vapour pressure to match, so the boiling point rises. This is why water boils below 100 °C on a mountain.

Question 16Matter and Its Nature: States, Classification, and Separation

A mixture of ethanol and water is heated and the vapour is condensed. Which statement about the distillate collected first is correct?

  1. It is richer in water because water has the lower boiling point.
  2. It contains only pure ethanol in a single simple distillation.
  3. It is richer in ethanol because ethanol is more volatile than water. Correct answer.
  4. It contains ethanol and water in exactly the same ratio as the original mixture.

Explanation

Ethanol has a lower boiling point than water and is more volatile, so its vapour predominates in the early distillate. The condensed liquid is therefore enriched in ethanol compared with the original mixture. Simple distillation cannot, however, give absolutely pure ethanol because the components form a constant-boiling mixture.

Question 17Matter and Its Nature: States, Classification, and Separation

Which pair of substances can be separated by using a magnet?

  1. Iron filings mixed with sulfur powder Correct answer.
  2. Sand mixed with chalk powder
  3. Ethanol mixed with water
  4. Salt dissolved in water

Explanation

Iron is ferromagnetic and is attracted by a magnet, whereas sulfur is not, so a magnet lifts the iron out of the mixture. The other pairs contain no magnetic component and must be separated by filtration, evaporation or distillation.

Question 18Matter and Its Nature: States, Classification, and Separation

A sample of muddy water is left undisturbed and clear water is then poured off the top. Which pair of processes has been used?

  1. Distillation followed by condensation
  2. Filtration followed by evaporation
  3. Sublimation followed by crystallisation
  4. Sedimentation followed by decantation Correct answer.

Explanation

Undisturbed mud particles settle to the bottom under gravity, which is sedimentation. Carefully pouring the clear liquid off the settled solid is decantation. No filter, heat or change of state is involved in this procedure.

Question 19Matter and Its Nature: States, Classification, and Separation

Which statement correctly distinguishes an element from a compound?

  1. An element always exists as single atoms, while a compound always exists as ions.
  2. An element has a variable composition, while a compound has a fixed composition.
  3. An element contains only one kind of atom, while a compound contains two or more elements chemically combined. Correct answer.
  4. An element can be broken down by chemical means, while a compound cannot.

Explanation

An element consists of only one type of atom and cannot be decomposed into simpler substances by chemical means. A compound contains two or more elements chemically combined in a fixed ratio, and can be broken down into those elements. Elements such as oxygen and sulfur exist as molecules, so single atoms are not required.

Question 20Matter and Its Nature: States, Classification, and Separation

Which example is a heterogeneous mixture?

  1. Carbon dioxide gas
  2. A sample of brass
  3. Aqueous copper(II) sulfate solution
  4. Oil and water shaken together and allowed to stand in a separating funnel Correct answer.

Explanation

Oil and water are immiscible and form two separate visible layers, so the system is heterogeneous. Copper(II) sulfate solution and brass are uniform mixtures, and carbon dioxide is a pure compound rather than a mixture.

Question 21Matter and Its Nature: States, Classification, and Separation

A technician needs to recover solid potassium nitrate from its aqueous solution while keeping the crystals reasonably large and pure. Which method is most suitable?

  1. Centrifugation of the solution
  2. Filtration of the solution through filter paper
  3. Rapid evaporation to complete dryness over a strong flame
  4. Slow crystallisation by controlled cooling of a saturated solution Correct answer.

Explanation

Slow cooling of a saturated solution allows crystals to grow gradually, giving larger and purer crystals because impurities tend to remain in the mother liquor. Rapid evaporation to dryness gives a fine impure crust and may decompose the salt. Filtration and centrifugation cannot remove a dissolved solute.

Question 22Matter and Its Nature: States, Classification, and Separation

Two colourless liquids are mixed and the mixture becomes warm, and the resulting liquid can no longer be separated by distillation into the original two liquids. What does this suggest?

  1. The liquids have sublimed into a gas.
  2. A chemical reaction has occurred, forming a new substance. Correct answer.
  3. The liquids have formed a heterogeneous mixture.
  4. A physical mixing has occurred, since warming always accompanies mixing.

Explanation

An exothermic change together with the formation of a product that cannot be separated by physical means indicates a chemical reaction. The evolution of heat and the loss of the original components' physical behaviour both point to a new substance. Simple mixing of liquids does not usually release significant heat or prevent distillation.

Question 23Matter and Its Nature: States, Classification, and Separation

A mixture contains ammonium chloride, sand and sodium chloride. Which sequence of steps will separate all three substances?

  1. Heat to sublime ammonium chloride, then add water, filter the sand, then evaporate the filtrate Correct answer.
  2. Add water and distil, then filter the distillate to recover the sand
  3. Heat to sublime ammonium chloride, then evaporate the residue directly without adding water
  4. Add water and filter first, then heat the residue to sublime ammonium chloride, then evaporate

Explanation

Ammonium chloride sublimes on gentle heating and can be collected as a sublimate, leaving sand and sodium chloride. Adding water dissolves the sodium chloride, filtration removes the insoluble sand, and evaporation of the filtrate recovers the sodium chloride. The order matters because water would dissolve the ammonium chloride and prevent its easy recovery.

Question 24Matter and Its Nature: States, Classification, and Separation

A liquid is heated and its temperature is plotted against time. The graph shows a plateau before the liquid begins to boil and a second plateau during boiling. What explains the first plateau?

  1. The liquid is freezing because heat is being removed.
  2. The liquid is at its boiling point but the vapour pressure has not yet reached the external pressure. Correct answer.
  3. The liquid is absorbing latent heat of vaporisation while its temperature stays constant.
  4. The heating source has been switched off during that interval.

Explanation

The first plateau occurs when the liquid reaches its boiling point; the temperature remains steady while the liquid's vapour pressure rises to equal the external pressure and bubbles can form throughout the liquid. The second plateau corresponds to the latent heat of vaporisation during boiling.

Question 25Atomic Structure and Chemical Bonding

According to Bohr's model of the hydrogen atom, what happens when an electron moves from a higher-energy orbit to a lower-energy orbit?

  1. A photon is emitted with energy equal to the difference between the two orbits Correct answer.
  2. The nucleus emits an alpha particle to conserve energy
  3. The electron's mass is converted entirely into kinetic energy
  4. A photon is absorbed with energy equal to the sum of the two orbits

Explanation

In Bohr's model each orbit has a fixed energy, and the electron cannot occupy values between them. When it drops to a lower orbit, the energy difference is released as a single photon whose energy equals that gap. This explains the discrete line spectrum of hydrogen.

Question 26Atomic Structure and Chemical Bonding

Which statement correctly describes the arrangement of particles in a neutral atom of chlorine-35?

  1. 35 protons, 35 neutrons, 17 electrons
  2. 17 protons, 17 neutrons, 17 electrons
  3. 17 protons, 18 neutrons, 17 electrons Correct answer.
  4. 18 protons, 17 neutrons, 18 electrons

Explanation

The atomic number of chlorine is 17, so every chlorine atom has 17 protons and, when neutral, 17 electrons. The mass number 35 is the sum of protons and neutrons, giving 35 minus 17 equals 18 neutrons.

Question 27Atomic Structure and Chemical Bonding

Two atoms are isotopes of the same element. Which quantity must be identical for both atoms?

  1. Number of neutrons
  2. Number of protons Correct answer.
  3. Mass number
  4. Number of nucleons

Explanation

Isotopes are atoms of the same element, so they share the same atomic number and therefore the same number of protons. They differ only in the number of neutrons, which changes the mass number.

Question 28Atomic Structure and Chemical Bonding

Which pair of elements is most likely to form an ionic bond with each other?

  1. Sodium and chlorine Correct answer.
  2. Chlorine and chlorine
  3. Carbon and oxygen
  4. Nitrogen and hydrogen

Explanation

Ionic bonding typically occurs between a metal with low ionisation energy and a non-metal with high electron affinity. Sodium is a group 1 metal that readily loses one electron, and chlorine is a halogen that readily gains one. The resulting ions are held by electrostatic attraction.

Question 29Atomic Structure and Chemical Bonding

What is the maximum number of electrons that the second electron shell (n = 2) can hold?

  1. 8 Correct answer.
  2. 32
  3. 18
  4. 2

Explanation

The capacity of a shell is given by 2n squared. For n = 2 this gives 2 times 4, which is 8 electrons, distributed over one 2s and three 2p orbitals.

Question 30Atomic Structure and Chemical Bonding

An atom of element X has the electron configuration 2, 8, 7. In which group of the periodic table does X belong?

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

Explanation

The 7 outer electrons indicate a halogen, which occupies group 17 of the modern periodic table. The older notation labels this same group as group VII. The element is chlorine.

Question 31Atomic Structure and Chemical Bonding

Why does the first ionisation energy generally increase across a period from left to right?

  1. The nuclear charge increases while the outer electron remains in roughly the same shell Correct answer.
  2. The number of electron shells increases, shielding the outer electron more
  3. The atomic radius increases, weakening the attraction for outer electrons
  4. The neutron-to-proton ratio decreases, destabilising the atom

Explanation

Across a period, protons are added to the nucleus while outer electrons enter the same shell, so shielding stays roughly constant. The growing effective nuclear charge binds the outer electron more tightly. Removing that electron therefore requires more energy.

Question 32Atomic Structure and Chemical Bonding

Which molecule contains a polar covalent bond but is overall non-polar because of its geometry?

  1. Hydrogen chloride, HCl
  2. Carbon dioxide, CO2 Correct answer.
  3. Water, H2O
  4. Ammonia, NH3

Explanation

In CO2 the two carbon-oxygen bonds are polar, but the molecule is linear and the two bond dipoles point in opposite directions. They cancel, giving zero net dipole moment. The other listed molecules have asymmetric shapes, so their bond dipoles do not cancel.

Question 33Atomic Structure and Chemical Bonding

How many sigma and pi bonds are present in a molecule of ethene, C2H4?

  1. 5 sigma and 2 pi
  2. 4 sigma and 1 pi
  3. 5 sigma and 1 pi Correct answer.
  4. 6 sigma and 1 pi

Explanation

Ethene has four carbon-hydrogen single bonds and one carbon-carbon double bond. Each single bond is one sigma bond, and the double bond consists of one sigma plus one pi bond. That gives 4 + 1 = 5 sigma bonds and 1 pi bond.

Question 34Atomic Structure and Chemical Bonding

According to VSEPR theory, what is the shape of the methane molecule, CH4?

  1. Tetrahedral Correct answer.
  2. Bent
  3. Trigonal pyramidal
  4. Square planar

Explanation

Carbon in methane has four bonding pairs of electrons and no lone pairs. VSEPR theory places four electron pairs as far apart as possible, giving a tetrahedral arrangement with bond angles of about 109.5 degrees.

Question 35Atomic Structure and Chemical Bonding

Which species has the electron configuration 1s2 2s2 2p6?

  1. A chloride ion, Cl-
  2. A sodium ion, Na+
  3. A magnesium atom, Mg
  4. An oxide ion, O2- Correct answer.

Explanation

The configuration 1s2 2s2 2p6 holds 10 electrons, matching the neon core. An oxygen atom has 8 electrons, and gaining two electrons gives the oxide ion 10 electrons.

Question 36Atomic Structure and Chemical Bonding

An element has two naturally occurring isotopes. Isotope A has mass 10 u and abundance 20 percent; isotope B has mass 11 u and abundance 80 percent. What is the relative atomic mass of the element?

  1. 10.2 u
  2. 10.8 u Correct answer.
  3. 11.0 u
  4. 10.5 u

Explanation

Relative atomic mass is the abundance-weighted average of the isotope masses. Multiplying gives 0.20 times 10 equals 2.0 and 0.80 times 11 equals 8.8, and adding these yields 10.8 u.

Question 37Atomic Structure and Chemical Bonding

Which explanation best accounts for the very low reactivity of the noble gases?

  1. Their nuclei contain too many neutrons to form bonds
  2. Their atoms are too large to approach other atoms closely
  3. Their atoms have a full outer electron shell, so they neither gain nor lose electrons readily Correct answer.
  4. They have only one electron in their outer shell, which is easily lost

Explanation

Noble gases have complete outer shells, so there is no energetic advantage in sharing or transferring electrons. This stable configuration is why they exist mainly as monatomic gases.

Question 38Atomic Structure and Chemical Bonding

Which of the following correctly lists the bonds in order of increasing polarity, based on electronegativity differences?

  1. H-F, then H-Cl, then H-H
  2. H-H, then H-Cl, then H-F Correct answer.
  3. H-Cl, then H-H, then H-F
  4. H-H, then H-F, then H-Cl

Explanation

Bond polarity grows with the electronegativity difference between the two atoms. A hydrogen-hydrogen bond has zero difference, hydrogen-chlorine has a moderate difference, and hydrogen-fluorine has the largest difference of the three.

Question 39Atomic Structure and Chemical Bonding

A magnesium atom loses two electrons to form Mg2+. Compared with the neutral atom, the ion has:

  1. The same radius, because only the charge changes
  2. A larger radius, because electron-electron repulsion is reduced
  3. A smaller radius, because the same nuclear charge attracts fewer electrons Correct answer.
  4. A larger radius, because the nucleus has gained protons

Explanation

When a metal atom loses electrons, the remaining electrons are pulled more strongly by the unchanged nuclear charge. The loss of an entire outer shell also reduces the size. Cations are therefore smaller than their parent atoms.

Question 40Atomic Structure and Chemical Bonding

Which set of quantum numbers correctly describes an electron in a 3p orbital?

  1. n = 3, l = 2, ml = 0
  2. n = 3, l = 1, ml = -1 Correct answer.
  3. n = 3, l = 0, ml = 0
  4. n = 2, l = 1, ml = +1

Explanation

For a 3p orbital the principal quantum number is 3 and the p subshell corresponds to l = 1. The magnetic quantum number can take any value from -1 to +1, so ml = -1 is allowed.

Question 41Atomic Structure and Chemical Bonding

Why does the ionic compound sodium chloride conduct electricity when molten but not when solid?

  1. Melting causes the ions to share electrons and form covalent bonds
  2. In the molten state the ions become mobile and can migrate to the electrodes Correct answer.
  3. The solid contains no charged particles at all
  4. Melting converts the ions into free electrons that carry the current

Explanation

In solid sodium chloride the ions are locked in a rigid lattice, so they cannot move to carry charge. Melting breaks the lattice and frees the ions to migrate towards the electrodes, allowing conduction.

Question 42Atomic Structure and Chemical Bonding

Successive ionisation energies of an element are 738, 1451, 7733, 10540 and 13630 kJ per mole. To which group does the element most likely belong?

  1. Group 1
  2. Group 2 Correct answer.
  3. Group 17
  4. Group 13

Explanation

The large jump occurs between the second and third ionisation energies, showing that the third electron comes from a much more tightly bound inner shell. This indicates two relatively easy outer electrons, characteristic of group 2 metals such as magnesium.

Question 43Atomic Structure and Chemical Bonding

Which description of metallic bonding best explains why metals are malleable and conduct electricity?

  1. A lattice of positive ions is held together by a sea of delocalised electrons Correct answer.
  2. Alternating positive and negative ions are held by strong electrostatic forces
  3. Neutral atoms are joined by directional covalent bonds in a rigid network
  4. Positive ions are fixed in place while shared electrons jump between them

Explanation

In the electron-sea model, metal cations occupy lattice sites while valence electrons are delocalised over the whole structure. Because the bonding is non-directional, layers of ions can slide without breaking the structure, and the mobile electrons carry current.

Question 44Atomic Structure and Chemical Bonding

The hydrogen molecule, H2, is held together by a covalent bond. Which statement best explains why this bond forms?

  1. Electrostatic repulsion between the two nuclei provides the binding force
  2. Each hydrogen atom donates its electron completely to the other atom
  3. The two nuclei fuse to form a helium nucleus during bond formation
  4. Overlap of the two 1s orbitals allows the electrons to be shared and lowers the total energy Correct answer.

Explanation

As two hydrogen atoms approach, their 1s orbitals overlap and the two electrons occupy a shared bonding region between the nuclei. This arrangement lowers the energy of the system compared with two isolated atoms.

Question 45Chemical Reactions, Acids, Bases, and Salts

Which gas is produced when dilute hydrochloric acid reacts with zinc granules?

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

Explanation

Reactive metals such as zinc displace hydrogen from dilute acids, so bubbles of hydrogen gas are released and zinc chloride forms in solution. Oxygen, carbon dioxide and chlorine are not produced in this metal-acid reaction.

Question 46Chemical Reactions, Acids, Bases, and Salts

A solution turns blue litmus paper red. Which statement about this solution is correct?

  1. It has a pH greater than 7.
  2. It has a pH less than 7. Correct answer.
  3. It is neutral with a pH of exactly 7.
  4. It contains no hydrogen ions.

Explanation

Acids turn blue litmus red, and acidic solutions have a pH below 7 because they contain hydrogen ions in excess. Neutral solutions leave litmus unchanged and alkaline solutions turn red litmus blue.

Question 47Chemical Reactions, Acids, Bases, and Salts

Which of the following is the correct formula of common salt?

  1. NaClO
  2. CaCl2
  3. NaCl Correct answer.
  4. KCl

Explanation

Common salt is sodium chloride, formed from one sodium ion and one chloride ion, giving the formula NaCl. The other formulas belong to different compounds used for other purposes.

Question 48Chemical Reactions, Acids, Bases, and Salts

When carbon dioxide gas is passed through lime water, the lime water first turns milky. Which compound causes this milky appearance?

  1. Calcium chloride
  2. Sodium carbonate
  3. Carbon monoxide
  4. Calcium carbonate Correct answer.

Explanation

Carbon dioxide reacts with calcium hydroxide in lime water to form insoluble calcium carbonate, which appears as a white precipitate. Excess carbon dioxide later dissolves this precipitate.

Question 49Chemical Reactions, Acids, Bases, and Salts

Which ion is responsible for the basic nature of a solution of sodium hydroxide?

  1. Hydroxide ion Correct answer.
  2. Hydrogen ion
  3. Sodium ion
  4. Chloride ion

Explanation

Bases are substances that release hydroxide ions in water, and these ions neutralise hydrogen ions from acids. Sodium ions are spectator ions in neutralisation and do not cause basicity.

Question 50Chemical Reactions, Acids, Bases, and Salts

Which type of reaction is represented by the equation AgNO3 + NaCl -> AgCl + NaNO3?

  1. Combination
  2. Displacement of a metal
  3. Decomposition
  4. Double displacement Correct answer.

Explanation

The two compounds exchange their ions, silver taking chloride and sodium taking nitrate, so this is a double displacement or precipitation reaction. A white precipitate of silver chloride is formed.