Explanation:

The correct answer is: D. Dalton's atomic theory

Dalton's atomic theory is about the nature of matter, stating that all matter is made of tiny indivisible particles called atoms. It is not explained by the kinetic theory of gases.

Here's why the other answers are incorrect:

• A. Boyle's law: This law (pressure × volume = constant at fixed temperature) can be explained using the motion of gas particles in the kinetic theory.


• B. Charles' law: This law (volume ∝ temperature at constant pressure) is also explained by the kinetic theory, since heating increases particle motion.


• C. Gay-Lussac's law: This law (pressure ∝ temperature at constant volume) can be explained by faster-moving particles hitting container walls more often.

Explanation:

The correct answer is: A. Methane

Methane (CH₄) makes up most of natural gas (about 70–90%). It is the simplest hydrocarbon and the main fuel used for heating and electricity generation.

Here's why the other answers are incorrect:

• B. Ethane: Present in natural gas, but only in small amounts compared to methane.


• C. Butane: Found in liquefied petroleum gas (LPG), not the main part of natural gas.


• D. Propane: Also common in LPG, but not the major component of natural gas.

Explanation:

The correct answer is: B. Involves decomposition

Thermal cracking is a process where large alkane molecules break down (decompose) into smaller hydrocarbons, such as alkanes and alkenes. It is used in petroleum refining to produce more useful products like gasoline and ethene.

Here's why the other answers are incorrect:

• A. Is an exothermic process: Cracking requires heat, so it is endothermic, not exothermic.


• C. Produces only small alkanes: Cracking produces both alkanes and alkenes, not just alkanes.


• D. Requires hydrogen: Hydrogen is not required in thermal cracking (it is used in hydrocracking, which is a different process).

Explanation:

The correct answer is: C. Incomplete combustion of petrol

Carbon deposits form in exhaust pipes when petrol burns without enough oxygen. Instead of forming carbon dioxide, some carbon remains as soot, which builds up in the exhaust system.

Here's why the other answers are incorrect:

• A. Contamination of petrol with diesel: This may affect engine performance but does not directly cause carbon deposits.


• B. Presence of carbon in petrol: All hydrocarbons contain carbon, but complete combustion should produce carbon dioxide, not deposits.


• D. Presence of additives in petrol: Additives are designed to improve performance, not to cause carbon buildup.

Explanation:

The correct answer is: B. 0.5

In CuCl₂, copper exists as Cu²⁺. This means 2 moles of electrons (2 Faradays) are needed to deposit 1 mole of copper. Therefore, passing 1 Faraday will deposit 0.5 moles of copper.

Here's why the other answers are incorrect:

• A. 0.25: Too small — 1 Faraday provides enough charge to deposit more than this.


• C. 1: This would require 2 Faradays of charge, not 1.


• D. 2: Impossible — it would require 4 Faradays of charge.

Explanation:

The correct answer is: C. The cracking of hydrocarbons

Cracking breaks down large hydrocarbon molecules (such as long-chain alkanes) into smaller, more useful molecules like alkanes and alkenes. This is the main industrial method of producing alkenes.

Here's why the other answers are incorrect:

• A. Combustion of alkanes: This produces carbon dioxide and water, not alkenes.


• B. Polymerization reactions: These join small alkene molecules together, rather than producing them.


• D. Addition of hydrogen to unsaturated vegetable oils: This process (hydrogenation) removes double bonds, making alkenes turn into alkanes, not the other way around.

Explanation:

The correct answer is: C. Applied chemistry

Petrochemistry involves converting crude oil and natural gas into useful products such as plastics, fuels, and fertilizers. It is considered applied chemistry because it uses chemical principles for practical, industrial purposes.

Here's why the other answers are incorrect:

• A. Biochemistry: This studies chemical processes in living organisms, not petroleum products.


• B. Pure chemistry: This focuses on knowledge for its own sake, not direct industrial applications.


• D. Environmental chemistry: This deals with chemical effects on the environment, not processing crude oil.

Explanation:

The correct answer is: A. Intermediates

Intermediates are formed during some steps of a reaction mechanism and then used up in later steps. They do not appear in the overall balanced equation because they are temporary species.

Here's why the other answers are incorrect:

• B. Reactants: These are the starting materials of the overall reaction, not temporary species.


• C. Inhibitors: These slow down or stop reactions but are not necessarily part of the reaction pathway.


• D. Products: These are the final substances formed after the reaction is complete, not short-lived species.

Explanation:

The correct answer is: A. Pentane has five isomers

Pentane (C₅H₁₂) has three structural chain isomers (n-pentane, isopentane, and neopentane) and additional stereoisomers, making a total of five isomers. This makes option A correct.

Here's why the other answers are incorrect:

• B. Butane has a lower boiling point than propane: Incorrect — butane has a higher boiling point than propane because it has more carbon atoms and stronger intermolecular forces.


• C. Addition reactions occur between alkanes and chlorine: Wrong — alkanes undergo substitution reactions with chlorine, not addition reactions.


• D. An alkane with 49 carbon atoms contains 100 hydrogen atoms: Incorrect — the general formula for alkanes is C_nH_2n+2. For n = 49, hydrogen atoms = 2(49) + 2 = 100, but this statement misrepresents context since alkanes with such a formula are not normally expressed that way in simple multiple-choice chemistry.

Explanation:

The correct answer is: B. Phenolphthalein

Phenolphthalein is best for titrating a weak acid like ethanoic acid with a strong base like sodium hydroxide. It changes color in the basic pH range, which accurately shows the endpoint of this titration.

Here's why the other answers are incorrect:

• A. Screened methyl orange: Its color change occurs too early in the acidic range and does not match the endpoint for a weak acid–strong base titration.


• C. Methyl orange: Also changes color in the acidic range, not suitable for this type of titration.


• D. Methyl red: Changes color at a pH range too low to accurately reflect the endpoint here.

Explanation:

The correct answer is: C. Cu²⁺(aq) + 2e⁻ → Cu(s)

In this reaction, copper ions gain two electrons to form solid copper. This gain of electrons is a reduction process.

Here's why the other answers are incorrect:

• A. CuSO₄(s) + H₂O(l) → …: This is not a proper reduction half-equation.


• B. Cu²⁺(aq) + e⁻ → Cu(s): Only one electron is shown, but copper needs two.


• D. Zn(s) → Zn²⁺(aq) + 2e⁻: This is an oxidation half-equation, not reduction.

Explanation:

The correct answer is: B. 0.74 mol dm⁻³

Step-by-step:

• 10.5 g of Na₂SO₄ is in 100 cm³ (which is 0.1 dm³).


• Molar mass of Na₂SO₄ = 142 g/mol.


• Moles = 10.5 ÷ 142 = 0.0739 mol.


• Concentration = 0.0739 ÷ 0.1 = 0.739 mol/dm³ ≈ 0.74 mol/dm³.

Here's why the other answers are incorrect:

• A. 2.15 mol dm⁻³: Much higher than the correct value, wrong calculation.


• C. 0.60 mol dm⁻³: Lower than the actual solubility.


• D. 0.57 mol dm⁻³: Also too low, does not match the mole ratio.

Explanation:

The correct answer is: A. sodium trioxocarbonate (IV)

Sodium trioxocarbonate (IV), also called sodium carbonate, is crystalline but does not contain water of crystallization.

Here's why the other answers are incorrect:

• B. Potassium trioxonitrate (V): Exists as a salt but not anhydrous in this context.


• C. Iron (II) tetraoxosulphate (VI): Usually crystallizes with water molecules.


• D. Sodium tetraoxosulphate (VI): Often forms hydrates (like Na₂SO₄·10H₂O).

Explanation:

The correct answer is: B. Neutral

Ethanoic acid (a weak acid) reacts with sodium hydroxide (a strong base) to form sodium acetate. The strong base neutralizes the weak acid, producing a neutral salt solution.

Here's why the other answers are incorrect:

• A. Amphoteric: Amphoteric substances can act as both acids and bases, not the case here.


• C. Acidic: The strong base completely neutralizes the acid, so it is not acidic.


• D. Basic: Excess base is not present, so the solution is not basic.

Explanation:

The correct answer is: C. CH₃COOC₂H₅ + H₂O → CH₃COO⁻ + CH₃CH₂OH

The hydrolysis of an ester (alkanoate) breaks the ester bond using water, forming an alcohol and a carboxylate ion. In this case, ethyl ethanoate reacts with water to form acetate ions and ethanol.

Here's why the other answers are incorrect:

• A. This shows neutralization, not ester hydrolysis.


• B. This is esterification, the opposite of hydrolysis.


• D. The products are written incorrectly (CH₂COOH is not correct).

Explanation:

The correct answer is: D. Rate of reaction is proportional to the number of effective collisions

Collision theory states that particles must collide with sufficient energy and proper orientation to react. Only these "effective collisions" cause reactions. The more effective collisions there are, the faster the reaction rate.

Here's why the other answers are incorrect:

• A. Not all collisions cause reactions; most are ineffective.


• B. Ineffective collisions do not cause chemical change.


• C. Collisions do not just split molecules; they need enough energy to overcome activation energy.

Explanation:

The correct answer is: A. React with the gas

Ammonia reacts with concentrated sulphuric acid and calcium chloride instead of being simply dried. This changes its composition, making them unsuitable drying agents.

Here's why the other answers are incorrect:

• B. Pollute the gas: The issue is not pollution but chemical reaction.


• C. Are poisonous: Toxicity is not the reason they can’t be used here.


• D. Are corrosive: Corrosiveness is unrelated to their reaction with ammonia.

Explanation:

The correct answer is: B. Cl₂ + 2NaF → 2NaCl + F₂

Fluorine is more reactive than chlorine, so chlorine cannot displace fluorine from sodium fluoride. Therefore, this reaction is not possible.

Here's why the other answers are correct:

• A. Chlorine oxidizes hydrogen sulphide to sulphur, forming HCl.


• C. Chlorine reacts with calcium hydroxide to form bleaching powder (CaOCl₂).


• D. Chlorine reacts with sodium hydroxide to form NaCl and NaClO (disproportionation reaction).

Explanation:

The correct answer is: A. 5

Iron (Fe) has atomic number 26, with configuration [Ar] 3d⁶ 4s². For Fe³⁺, three electrons are removed (two from 4s, one from 3d), leaving 3d⁵. Each of the five 3d orbitals has one unpaired electron, so there are 5 unpaired electrons.

Here's why the other answers are incorrect:

• B. 4: Underestimates the number of unpaired electrons.


• C. 3: Not consistent with Hund’s rule for 3d⁵.


• D. 2: Too low; misses the actual configuration.

Explanation:

The correct answer is: D. Electronegativity decreases

As you go down Group II, atoms get bigger because more shells are added. The outer electrons are farther from the nucleus and are more shielded, so the nucleus pulls them less strongly. This makes electronegativity decrease.

Here's why the other answers are incorrect:

• A. Melting point increases: This is not regular; it goes up and down.


• B. Shielding effect decreases: Shielding actually increases, not decreases.


• C. Ionization energy increases: It decreases because outer electrons are easier to remove.

Explanation:

The correct answer is: D. Sodium

Sodium has one outer electron in the 3s orbital, so it is an s-block element.

Here's why the other answers are incorrect:

• A. Aluminium: Its outer electrons are in the p orbital.


• B. Phosphorus: Its outer electrons are in the p orbital.


• C. Carbon: Its outer electrons are in the p orbital.

Explanation:

The correct answer is: B. Electronegativity

Electronegativity is how strongly an atom pulls shared electrons in a bond. If two atoms have different electronegativity values, the bond will be uneven, making the molecule polar.

Here's why the other answers are incorrect:

• A. Ionization energy: This is about removing electrons, not bond polarity.


• C. Electron affinity: This is about gaining electrons, not polarity.


• D. Atomic radius: This tells us the size of an atom, not if a bond is polar.

Explanation:

The correct answer is: C. Open-mindedness

Open-mindedness is an attitude of a good scientist, but it is not one of the formal steps of the scientific method. The main steps are: observation, problem identification, hypothesis, experiment, data collection, and analysis.

Here's why the other answers are correct steps:

• A. Analysis: Scientists study data carefully to make conclusions.


• B. Experimentation: Experiments are done to test ideas (hypotheses).


• D. Problem identification: The process starts by stating the problem clearly.

Explanation:

The correct answer is: D. Electrons

Isoelectronic species are atoms or ions that have the same number of electrons. For example: O²⁻, F⁻, Na⁺, and Ne all have 10 electrons.

Here's why the other answers are incorrect:

• A. Ions: Isoelectronic species may not all be ions.


• B. Protons: Each element has a different number of protons.


• C. Neutrons: Isotopes differ in neutrons, not isoelectronic species.

Explanation:

The correct answer is: B. 65.50

To calculate the relative atomic mass:

• (65 × 0.60) + (66 × 0.40)
• = 39 + 26.4
• = 65.4 ≈ 65.50

So, the average relative atomic mass is 65.50.

Explanation:

The correct answer is: A. C₂H₆ and C₄H₁₀

C₂H₆ (ethane) and C₄H₁₀ (butane) are both alkanes. They belong to the same homologous series because they have the same general formula and the same functional group.

Members of a homologous series differ by a CH₂ unit.

Why others are wrong:

• B. C₄H₁₀ and C₅H₁₀: The first is an alkane, the second is an alkene.


• C. C₂H₄ and C₄H₁₀: One is an alkene, the other is an alkane.


• D. C₃H₈ and C₃H₆: One is an alkane, the other is an alkene.

Explanation:

The correct answer is: D. Flooding

Global warming causes the polar ice caps to melt. This makes sea levels rise, which increases the chance of flooding in low-lying coastal areas.

Why others are wrong:

• A. Water pollution: This is caused by waste, not global warming.


• B. High humidity: Not a direct effect of global warming.


• C. Air pollution: This causes global warming but is not a result of it.

Explanation:

The correct answer is: B. Oxygen

According to Graham’s Law, gases with higher molar mass diffuse more slowly.

• Oxygen (O₂): 32 g/mol
• Nitrogen (N₂): 28 g/mol
• Ammonia (NH₃): 17 g/mol
• Methane (CH₄): 16 g/mol

Since oxygen has the highest molar mass, it diffuses the slowest.

Explanation:

The correct answer is: D. Nitrogen

Air has an average molar mass of about 29 g/mol. Nitrogen (N₂) has a molar mass of 28 g/mol, so it is slightly lighter (less dense) than air.

Why others are wrong:

• CO₂ = 44 g/mol (heavier than air)


• O₂ = 32 g/mol (heavier than air)


• Cl₂ = 71 g/mol (much heavier than air)

Explanation:

The correct answer is: A. H₂SO₄(aq)

Sulfuric acid (H₂SO₄) is a strong acid and ionizes completely in water. Each molecule produces 2 H⁺ ions and 1 SO₄²⁻ ion. This gives a large number of ions in solution, so it conducts electricity the best.

Why others are wrong:

• H₂CO₃: weak acid, gives few ions.


• NaOH: strong base, but produces fewer ions than H₂SO₄.


• CH₃COONa: salt of a weak acid, not as many free ions.

Explanation:

The correct answer is: D. Cations are discharged

At the cathode, cations (positively charged ions) gain electrons. This process is called reduction, and it discharges them as neutral atoms or molecules.

Here's why the other answers are incorrect:

• A. Anions are oxidized: Oxidation of anions happens at the anode, not the cathode.


• B. Cations are oxidized: Cations gain electrons (reduction), not lose them.


• C. Anions lose electrons: This is true for the anode, not the cathode.

Explanation:

The correct answer is: C. 0.80 g

We use the formula: moles = concentration × volume.

Convert 100.0 cm³ to dm³: 100.0 cm³ = 0.100 dm³.

Now, moles of NaOH = 0.20 × 0.100 = 0.020 mol.

Mass = moles × molar mass = 0.020 × 40.0 = 0.80 g.

Here's why the other answers are incorrect:

• A. 800.0 g: Too large, result of wrong unit conversion.


• B. 20.0 g: Error from skipping volume conversion.


• D. 0.02 g: Error from mixing up moles and mass.

Explanation:

The correct answer is: C. Polarity

When hydrogen bonds with a highly electronegative atom (like oxygen, fluorine, or nitrogen), the electrons are shared unequally. This causes polarity in the molecule.

Here's why the other answers are incorrect:

• A. Electrovalent bond: This is ionic bonding, not hydrogen with electronegative atoms.


• B. Metallic bond: Exists in metals, not in hydrogen compounds.


• D. Dipole: A dipole is the effect caused by polarity, not the bond itself.

Explanation:

The correct answer is: A. Cl₂

Cl₂ has a non-polar covalent bond because both chlorine atoms have the same electronegativity, so the electrons are shared equally.

Here's why the other answers are incorrect:

• B. HCl: Has a polar covalent bond due to the difference in electronegativity between H and Cl.


• C. NH₃: Polar molecule because of the electronegativity difference between N and H.


• D. H₂O: Polar covalent bonds exist due to the high electronegativity of oxygen compared to hydrogen.

Explanation:

The correct answer is: C. W and X only

Elements with lower ionization energy lose electrons more easily, which makes them more reactive with chlorine. W (12.0) and X (21.0) have the lowest ionization energies, so they react most readily with chlorine.

Here's why the other answers are incorrect:

• A. X and Z only: Z has a very high ionization energy (200.0), so it is not very reactive.


• B. W and Z only: Same issue—Z’s high ionization energy makes it less reactive.


• D. Y and Z only: Both Y (106.0) and Z (200.0) have high ionization energies, so they are much less reactive than W and X.

Explanation:

The correct answer is: D. 15

Vapour density is calculated using:

Vapour Density = Relative Molar Mass ÷ 2

So, 30 ÷ 2 = 15.

Here's why the other answers are incorrect:

• A. 60: This is double the molar mass, not half.


• B. 45: Incorrect division, not based on the correct formula.


• C. 30: That’s the molar mass itself, not the vapour density.

Explanation:

The correct answer is: A. 198 kJ of energy is absorbed

A positive ∆H means the reaction is endothermic, so energy is absorbed from the surroundings.

Here's why the other answers are incorrect:

• B. The reaction is exothermic: Wrong — exothermic reactions have negative ∆H.


• C. 198 kJ of energy is given off: This would be true for an exothermic reaction, not this one.


• D. The reaction container would feel warm: In an endothermic reaction, the container feels cool as heat is absorbed.

Explanation:

The correct answer is: D. Polymerization

The kinetic theory of matter is supported by physical processes that show particle motion, such as melting, diffusion, and evaporation.

Polymerization, on the other hand, is a chemical reaction where small molecules join to form larger ones. It does not provide evidence of particle motion in the same way.

Here's why the other answers are incorrect:

• A. Melting: Shows particles gaining enough energy to move more freely.


• B. Diffusion: Demonstrates random motion of particles spreading out.


• C. Evaporation: Particles at the surface gain enough energy to escape into gas form.

Explanation:

The correct answer is: C. An alkaline gas

Concentrated tetraoxosulphate (VI) acid (H₂SO₄) is used to dry alkaline gases such as ammonia because it removes water without reacting much with the gas. Calcium oxide cannot be used because it is basic and would react with the alkaline gas instead of just drying it.

Here’s why the other answers are incorrect:

• A. Acid anhydride: These react with water, but drying them with H₂SO₄ is not the main method.


• B. Deliquescent salt: These absorb water from the air; they are not dried using this method.


• D. Neutral salt: Neutral salts don’t require special drying with conc. H₂SO₄.

Explanation:

The correct answer is: B. Metallic bonds

In metallic bonding, positive metal ions are packed in a structure and surrounded by free-moving electrons (a "sea of electrons"). This is why metals can conduct electricity and be bent without breaking.

Here’s why the other answers are incorrect:

• A. Covalent bonds: These involve sharing electrons between atoms, not free electrons around ions.


• C. Dative bonds: These occur when one atom donates both electrons for a bond, not a sea of electrons.


• D. Ionic bonds: These are formed by transfer of electrons between atoms, creating positive and negative ions, not free-moving electrons.

Explanation:

The correct answer is: C. It is a strong oxidizing agent

Dilute trioxonitrate (V) acid (HNO₃) does not release hydrogen when reacting with metals because instead of forming hydrogen gas, it oxidizes the hydrogen into water or forms nitrogen oxides.

Here’s why the other answers are incorrect:

• A. Highly corrosive: Being corrosive does not stop hydrogen from forming.


• B. Reacts with the product: The issue is not reaction with hydrogen, but oxidation.


• D. No visible reaction: A reaction does occur, but the products are nitrogen oxides, not hydrogen gas.

Explanation:

The correct answer is: B. 0.0625

Molar mass of O₃ = 3 × 16 = 48 g/mol.
Moles = mass ÷ molar mass = 3.0 ÷ 48 = 0.0625 mol.

Here’s why the other answers are incorrect:

• A. 0.6250: This is 10× too large, likely from dividing wrongly.


• C. 0.0930: Incorrect calculation, not matching mass/molar mass.


• D. 0.0093: Too small, shows wrong division.

Explanation:

The correct answer is: B. Have vacant d-orbital

Copper(II) ions (Cu²⁺) can accept lone pairs of electrons because they have empty d-orbitals. This makes them able to form coordinate covalent bonds with ligands.

Here’s why the other answers are incorrect:

• A. Are coloured: Colour comes from d–d transitions, not from forming coordinate bonds.


• C. Are positively charged: Many ions are positive, but not all can form coordinate bonds.


• D. Have unpaired electrons: This explains magnetism, not coordinate bonding.

Explanation:

The correct answer is: A. 400 cm³

Using the formula: Concentration = moles ÷ volume.
Volume = moles ÷ concentration = 0.100 ÷ 0.250 = 0.4 dm³ = 400 cm³.

Here’s why the other answers are incorrect:

• B. 200 cm³: Half the correct value, from using wrong ratio.


• C. 100 cm³: Too small, from dividing wrongly.


• D. 20 cm³: Much too small, calculation error.

Explanation:

The correct answer is: C. The total kinetic energy of the gas is not affected by collision

In gases, molecules move freely and collide often. These collisions can change the energy of individual molecules, but the total kinetic energy of all the molecules stays the same as long as the temperature does not change. That means statement C is wrong, because collisions do affect how energy is shared.

Why the other options are correct:

• A. Constant motion: Gas molecules are always moving.




• B. Solubility: Gases dissolve less in water when temperature is high, so this statement is true in context.



• D. Low density: Gases are much less dense than solids or liquids of the same mass.

Explanation:

The correct answer is: D. HF, NH₃, SiH₄, CH₄

HF has the highest boiling point because it forms very strong hydrogen bonds.

NH₃ also makes hydrogen bonds, but they are weaker than those in HF, so its boiling point is lower than HF.

SiH₄ and CH₄ are nonpolar molecules, so they only have weak London forces, giving them much lower boiling points.

Order: HF > NH₃ > SiH₄ > CH₄

Explanation:

The correct answer is: A. There is a large decrease in the volume of a solid metal when pressure is applied to it

Solids like metals are almost incompressible, so their volume does not change much under pressure. This makes statement A incorrect.

Why the other statements are correct:

• B. Methane vs diamond: Carbon atoms in methane are farther apart than in diamond.


• C. Particle motion: Gas particles move faster than liquid particles.


• D. Freezing: When a liquid becomes a solid, energy is released.

Explanation:

The correct answer is: A. 30

Vapour density is found by dividing the relative molecular mass (RMM) by 2.

For C₂H₄O₂:

• C = 12 × 2 = 24
• H = 1 × 4 = 4
• O = 16 × 2 = 32

Total RMM = 24 + 4 + 32 = 60

Vapour density = 60 ÷ 2 = 30

Explanation:

The correct answer is: B. Crystallization

Crystallization separates salts when they have different solubility. The less soluble salt forms crystals first as the solution cools or the solvent evaporates.

Why the other options are wrong:

• A. Chromatography: Used for separating mixtures of liquids or gases, not salts.


• C. Distillation: Works for separating liquids based on boiling points, not solid salts.


• D. Evaporation: Removes the solvent but does not separate two salts with different solubility.

Explanation:

The correct answer is: C. Solvent extraction

Solvent extraction is used because iodine dissolves better in another solvent (like alcohol) than in tetrachloromethane. This makes it possible to pull out the iodine.

Why the other options are wrong:

• A. Filtration: Works only when separating solids from liquids, not dissolved iodine.


• B. Decantation: Used to separate liquids from settled solids, not dissolved substances.


• D. Fractional distillation: Separates liquids based on boiling points, not for iodine in solution.