Chemistry MCQs

Question #181

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The acid used in car batteries is:

A. Nitric acid

B. Phosphoric acid

C. Hydrochloric acid

D. Sulphuric acid

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Correct Answer: Option D

Explanation:
Lead-acid batteries (used in automobiles) contain dilute sulfuric acid (H₂SO₄) with specific gravity around 1.25-1.30 when fully charged. It acts as electrolyte and participates in the electrode reactions. Nitric acid is a strong oxidizing agent, HCl is not used because it would produce chlorine, phosphoric acid is in some fuel cells but not lead-acid batteries.

This question belongs to: Science chemistry

Question #182

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Aqua regia, which can dissolve gold and platinum, is a mixture of:

A. HNO₃ and H₂SO₄

B. HCl and H₂SO₄

C. HF and HCl

D. HCl and HNO₃ in ratio 3:1

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Correct Answer: Option D

Explanation:
Aqua regia (royal water) is a 3:1 mixture by volume of concentrated HCl and HNO₃. It generates nascent chlorine and nitrosyl chloride, which oxidize gold and platinum to soluble chloro complexes (e.g., HAuCl₄). Neither acid alone can dissolve these noble metals. Used for cleaning glassware and in etching. Must be prepared fresh and handled with extreme care.

This question belongs to: Science chemistry

Question #183

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Methanol is also known as:

A. Rubbing alcohol

B. Denatured alcohol

C. Grain alcohol

D. Wood alcohol

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Correct Answer: Option D

Explanation:
Methanol (CH₃OH) was historically produced by destructive distillation of wood, hence called wood alcohol. Ethanol is grain alcohol (from fermentation). Rubbing alcohol is isopropanol or denatured ethanol. Denatured alcohol is ethanol with added methanol or other substances to make it undrinkable. Methanol is toxic, used as solvent, fuel, and antifreeze.

This question belongs to: Science chemistry

Question #184

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The micelle formation by soap in water is possible due to:

A. Hydrophilic head and hydrophobic tail

B. Covalent bonding with dirt

C. Only hydrophobic interaction

D. Electrostatic repulsion

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Correct Answer: Option A

Explanation:
Soap molecules have a hydrophilic ionic head (COO⁻Na⁺) and a long hydrophobic hydrocarbon tail. In water, the tails aggregate away from water, forming a spherical micelle with heads outward. The hydrophobic core dissolves oily dirt, which is then washed away. This structure is stabilized by ion-dipole interactions. Detergents work similarly but with different head groups.

This question belongs to: Science chemistry

Question #185

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Cement sets into a hard mass when mixed with water due to:

A. Hydration and crystallization of silicates and aluminates

B. Oxidation

C. Evaporation of water

D. Polymerization

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Correct Answer: Option A

Explanation:
Cement undergoes hydration reactions: water reacts with cement compounds (C₃S, C₂S, C₃A) to form complex hydrated silicates and aluminates (e.g., C-S-H gel) along with Ca(OH)₂. This process causes setting and hardening, forming a rigid, rock-like mass. It is exothermic. Gypsum controls initial setting. Proper curing is necessary for strength development.

This question belongs to: Science chemistry

Question #186

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PVC (polyvinyl chloride) is used for making pipes and insulation because it is:

A. Conductor of electricity

B. Biodegradable

C. Highly flexible without additives

D. A good insulator and chemically resistant

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Correct Answer: Option D

Explanation:
PVC is a good electrical insulator, resistant to chemicals, water, and fire (self-extinguishing due to chlorine content), making it suitable for cable insulation, pipes, and medical tubing. It is not biodegradable. Flexibility is achieved by adding plasticizers, otherwise rigid. It is an addition polymer of vinyl chloride. Unplasticized PVC (uPVC) is used in construction.

This question belongs to: Science chemistry

Question #187

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Temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium. Boiling precipitates:

A. CaSO₄

B. CaCO₃

C. MgCl₂

D. CaCl₂

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Correct Answer: Option B

Explanation:
On boiling, soluble calcium bicarbonate decomposes: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. The precipitate is calcium carbonate (limestone/chalk). Magnesium bicarbonate similarly forms MgCO₃ or Mg(OH)₂. This removes Ca²⁺ and Mg²⁺ ions, softening the water. Permanent hardness (CaSO₄, CaCl₂) doesn't precipitate on boiling and needs chemical treatment.

This question belongs to: Science chemistry

Question #188

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Beta particles are:

A. Positively charged protons

B. High energy electrons

C. Neutrons

D. Helium nuclei

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Correct Answer: Option B

Explanation:
Beta particles are high-energy, high-speed electrons (β⁻) or positrons (β⁺) emitted from a radioactive nucleus during beta decay. In β⁻ decay, a neutron converts to a proton, emitting an electron and an antineutrino. Beta particles have moderate penetrating power; they can be stopped by a few millimeters of aluminum. They cause less ionization than alpha.

This question belongs to: Science chemistry

Question #189

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The concept of half-life applies to:

A. Only chemical reactions

B. First-order reactions only

C. Zero-order reactions only

D. All radioactive decay

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Correct Answer: Option D

Explanation:
Half-life is a characteristic of first-order kinetics, and all radioactive decay follows first-order kinetics. Hence it applies to all radioactive decay processes. Chemical reactions of first order also have constant half-life independent of initial concentration, but radioactive decay is the prime example. Zero-order half-life depends on initial concentration.

This question belongs to: Science chemistry

Question #190

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Dalton's atomic theory could NOT explain:

A. Existence of isotopes

B. Law of multiple proportions

C. Law of definite proportions

D. Law of conservation of mass

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Correct Answer: Option A

Explanation:
Dalton proposed that all atoms of a given element are identical in mass and properties. The discovery of isotopes (atoms of same element with different mass) contradicted this. Dalton's theory explained the three laws of chemical combination. Later models modified the theory. Subatomic particles and radioactivity also could not be explained by Dalton.

This question belongs to: Science chemistry

Question #191

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Which of the following is a correct match of the scientist and the discovery?

A. Chadwick – Proton

B. Bohr – Electron

C. J.J. Thomson – Neutron

D. Rutherford – Nucleus

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Correct Answer: Option D

Explanation:
Ernest Rutherford discovered the atomic nucleus through his gold foil experiment (1911). J.J. Thomson discovered the electron (1897). Chadwick discovered the neutron (1932). Bohr proposed the model of the atom with quantized energy levels (1913), not the electron. Rutherford also discovered the proton (1919). Naming discoveries correctly is important for competitive exams.

This question belongs to: Science chemistry

Question #192

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The element with atomic number 20 has the electronic configuration:

A. 2,8,8,2

B. 2,8,8,4

C. 2,8,10

D. 2,8,18,2

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Correct Answer: Option A

Explanation:
Atomic number 20 is calcium (Ca). Electron shells fill according to 2n²: K=2, L=8, M can hold 18 but fourth shell (N) starts after 8 electrons in M due to energy level considerations (Aufbau principle). So Ca configuration is 2,8,8,2. It has 2 valence electrons, belongs to Group 2, Period 4. Its nearest noble gas is Ar (2,8,8).

This question belongs to: Science chemistry

Question #193

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Which of the following does NOT contain ionic bond?

A. CaO

B. NaF

C. KCl

D. CH₄

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Correct Answer: Option D

Explanation:
CH₄ (methane) has covalent bonds where carbon shares electrons with four hydrogen atoms. CaO (Ca²⁺ O²⁻), KCl, and NaF are ionic compounds formed by electron transfer between a metal and a non-metal. Ionic bonds form when electronegativity difference is large. Covalent bonds typically between non-metals with similar electronegativities.

This question belongs to: Science chemistry

Question #194

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The bond in CO is actually a triple bond with a coordinate covalent bond. The total number of electrons shared between C and O in CO is:

A. 2

B. 4

C. 8

D. 6

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Correct Answer: Option D

Explanation:
CO has a triple bond: one sigma and two pi bonds, with a coordinate covalent character where oxygen donates a lone pair to carbon, forming a bond similar to triple bond. Total shared electrons = 6 (three pairs). Lewis structure shows :C≡O: with formal charges. The bond order is 3. It is isoelectronic with N₂ and CN⁻.

This question belongs to: Science chemistry

Question #195

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Which of the following trends is observed in Group 1 (alkali metals) down the group?

A. Atomic radius increases

B. Reactivity decreases

C. Ionization energy increases

D. Electronegativity increases

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Correct Answer: Option A

Explanation:
Down Group 1 (Li → Fr), atomic radius increases due to addition of electron shells. Ionization energy and electronegativity decrease. Reactivity with water increases because the outer electron is more easily lost. Density generally increases, melting/boiling points decrease. Cesium and francium are most reactive. The increase in radius is due to principal quantum number increase.

This question belongs to: Science chemistry

Question #196

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In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, Zn is:

A. Hydrolyzed

B. Oxidized

C. Reduced

D. Precipitated

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Correct Answer: Option B

Explanation:
Zinc loses electrons: Zn → Zn²⁺ + 2e⁻, thus it is oxidized (increase in oxidation state from 0 to +2). Copper ions gain electrons: Cu²⁺ + 2e⁻ → Cu, thus copper is reduced. Zn acts as the reducing agent, CuSO₄ as the oxidizing agent. This is a single displacement redox reaction. Zn is more reactive than Cu.

This question belongs to: Science chemistry

Question #197

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A solution has [H⁺] = 10⁻⁴ M. Its pH is:

A. 4

B. 1

C. 10

D. 7

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Correct Answer: Option A

Explanation:
pH = -log[H⁺] = -log(10⁻⁴) = 4. The solution is acidic. pOH = 14 - pH = 10, so [OH⁻] = 10⁻¹⁰ M. pH scale ranges 0-14 (typically). pH < 7 acidic, pH = 7 neutral, pH > 7 basic. Pure water has [H⁺] = 10⁻⁷ M, pH=7.

This question belongs to: Science chemistry

Question #198

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Which of the following salts is used in the manufacture of glass?

A. Sodium carbonate

B. Potassium nitrate

C. Ammonium chloride

D. Sodium chloride

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Correct Answer: Option A

Explanation:
Sodium carbonate (Na₂CO₃), also called soda ash, is a key ingredient in glass manufacturing. It lowers the melting point of silica (SiO₂) and provides sodium oxide. The glass batch consists of sand (SiO₂), soda ash (Na₂CO₃), and limestone (CaCO₃). Sodium chloride is table salt, potassium nitrate used in gunpowder, ammonium chloride in batteries/leclanche cells.

This question belongs to: Science chemistry

Question #199

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The corrosion of iron can be prevented by coating it with a layer of zinc. This process is called:

A. Anodizing

B. Tinning

C. Electroplating with silver

D. Galvanization

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Correct Answer: Option D

Explanation:
Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting. Zinc acts as sacrificial anode. Tinning is coating with tin (tin cans). Anodizing is an electrochemical process for aluminum to form protective oxide. Electroplating can be with any metal. Galvanized iron is used for roofing sheets, water pipes.

This question belongs to: Science chemistry

Question #200

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Carbon forms a large number of compounds due to its unique property of:

A. Electrovalency

B. Catenation and tetravalency

C. High electronegativity

D. Forming ionic bonds

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Correct Answer: Option B

Explanation:
Carbon's ability to form bonds with other carbon atoms (catenation) and its tetravalency (four valence electrons) allow it to form long chains, branches, and rings, leading to millions of organic compounds. The C-C bond is strong (bond energy ~348 kJ/mol). Silicon also shows catenation but to much lesser extent. Carbon also forms multiple bonds, enhancing diversity.

This question belongs to: Science chemistry

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