Chemistry MCQs

Question #541

Share Report

As we move from left to right across a period, the atomic radius generally:

A. Remains constant

B. Decreases

C. Increases

D. First increases then decreases

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Across a period, the atomic radius decreases. This is because the number of protons (nuclear charge) increases, pulling the electrons in the same shell closer to the nucleus, while the number of shells remains constant. This increases the effective nuclear charge experienced by the valence electrons.

This question belongs to: Science chemistry

Question #542

Share Report

The element with atomic number 17 belongs to which group and period?

A. Group 17, Period 3

B. Group 7, Period 2

C. Group 7, Period 3

D. Group 17, Period 2

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
The element with atomic number 17 is Chlorine. Its electronic configuration is 2, 8, 7. It has 3 shells, so it is in Period 3. It has 7 valence electrons, so it belongs to Group 17 (10 + 7 = 17 in modern IUPAC notation) along with fluorine, bromine, and iodine.

This question belongs to: Science chemistry

Question #543

Share Report

Which of the following has the highest ionization energy?

A. Al

B. Si

C. Na

D. Mg

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Ionization energy generally increases across a period due to increasing nuclear charge and decreasing atomic size. Among Na, Mg, Al, and Si (Period 3), Si has the highest effective nuclear charge and smallest size, thus requiring the maximum energy to remove the outermost electron from its gaseous state.

This question belongs to: Science chemistry

Question #544

Share Report

Mendeleev's periodic table faced several anomalies. Which of the following was one of them?

A. Isotopes were placed in different groups.

B. Hydrogen was given a fixed position in Group 1.

C. Cobalt and Nickel were placed in the wrong order of atomic mass.

D. Lanthanides and Actinides were placed in separate blocks.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Mendeleev placed Cobalt (atomic mass 58.9) before Nickel (atomic mass 58.7) to maintain chemical similarities, violating his own periodic law based on atomic mass. Isotopes weren't an issue then, and H's position was ambiguous, but the Co/Ni placement is a classic anomaly of his atomic mass-based table.

This question belongs to: Science chemistry

Question #545

Share Report

The tendency of an atom to gain electrons is known as:

A. Metallic character

B. Ionization energy

C. Electron affinity

D. Electropositivity

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Electron affinity is the energy change when an electron is added to a neutral gaseous atom. It represents the tendency to gain electrons. Ionization energy is the energy to remove an electron. Electropositivity and metallic character relate to the tendency to lose electrons and form positive ions.

This question belongs to: Science chemistry

Question #546

Share Report

Which of the following oxides is amphoteric?

A. SO₂

B. MgO

C. Na₂O

D. Al₂O₃

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Amphoteric oxides react with both acids and bases to form salts and water. Aluminum oxide (Al₂O₃) and Zinc oxide (ZnO) are classic examples. Na₂O and MgO are basic oxides that react only with acids, while SO₂ is an acidic oxide that reacts only with bases.

This question belongs to: Science chemistry

Question #547

Share Report

Assertion (A): The noble gases are placed in Group 18. Reason (R): They have a completely filled outermost shell (except Helium) and zero valency.

A. Both A and R are true but R is NOT the correct explanation of A.

B. Both A and R are true and R is the correct explanation of A.

C. A is true but R is false.

D. A is false but R is true.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Noble gases have completely filled valence shells (ns²np⁶, except He which is 1s²), making them highly stable and unreactive with a valency of zero. Because of this unique stability and distinct electronic configuration, they form a separate group, Group 18, in the modern periodic table.

This question belongs to: Science chemistry

Question #548

Share Report

In the reaction: 2PbO + C → 2Pb + CO₂, which substance is oxidized?

A. PbO

B. Pb

C. C

D. CO₂

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Oxidation is the gain of oxygen or loss of electrons. Here, Carbon (C) gains oxygen to form Carbon dioxide (CO₂), so Carbon is oxidized. Lead oxide (PbO) loses oxygen to form Lead (Pb), so PbO is reduced. This is a classic redox reaction where both processes occur simultaneously.

This question belongs to: Science chemistry

Question #549

Share Report

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

A. AgNO₃ + NaCl → AgCl + NaNO₃

B. 2H₂ + O₂ → 2H₂O

C. 2KClO₃ → 2KCl + 3O₂

D. Fe + CuSO₄ → FeSO₄ + Cu

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
A decomposition reaction is one where a single compound breaks down into two or more simpler substances. Heating potassium chlorate (KClO₃) breaks it down into potassium chloride and oxygen gas. A is combination, C is displacement, and D is double displacement.

This question belongs to: Science chemistry

Question #550

Share Report

The reaction between an acid and a base to form salt and water is called:

A. Sublimation

B. Precipitation

C. Neutralization

D. Oxidation

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Neutralization is a chemical reaction in which an acid and a base react quantitatively with each other to form a salt and water. For example, HCl + NaOH → NaCl + H₂O. It is generally an exothermic process, and the resulting solution has a pH closer to 7.

This question belongs to: Science chemistry

Question #551

Share Report

Which of the following reactions is a double displacement reaction?

A. CaCO₃ → CaO + CO₂

B. BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl

C. Zn + H₂SO₄ → ZnSO₄ + H₂

D. 2Mg + O₂ → 2MgO

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
In a double displacement reaction, ions of two compounds exchange places to form two new compounds. Here, Ba²⁺ and Na⁺ exchange their anions (Cl⁻ and SO₄²⁻) to form BaSO₄ (a white precipitate) and NaCl. This is also a precipitation reaction due to the formation of insoluble barium sulfate.

This question belongs to: Science chemistry

Question #552

Share Report

Rusting of iron is a chemical change because:

A. It can be reversed by heating.

B. A new substance, hydrated iron oxide, is formed.

C. It involves a change in state.

D. The color of iron changes.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Rusting is a chemical change because iron reacts with oxygen and moisture to form a completely new chemical substance, hydrated iron(III) oxide (Fe₂O₃·xH₂O), which has different chemical properties from iron and cannot be easily reversed by simple physical means like heating or cooling.

This question belongs to: Science chemistry

Question #553

Share Report

Identify the type of reaction: CuSO₄ + Fe → FeSO₄ + Cu.

A. Displacement

B. Decomposition

C. Combination

D. Double displacement

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
This is a single displacement reaction. Iron (Fe) is more reactive than Copper (Cu), so it displaces copper from its aqueous sulfate solution. The blue color of CuSO₄ fades, and a brown deposit of Cu forms. Reactivity series dictates that a more reactive metal displaces a less reactive one.

This question belongs to: Science chemistry

Question #554

Share Report

In a redox reaction:

A. Oxidation and reduction occur simultaneously.

B. Only oxidation occurs.

C. Only reduction occurs.

D. Neither oxidation nor reduction occurs.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Redox stands for reduction-oxidation. In any redox reaction, oxidation (loss of electrons) and reduction (gain of electrons) always occur simultaneously. The substance oxidized acts as a reducing agent, and the substance reduced acts as an oxidizing agent. One cannot happen without the other.

This question belongs to: Science chemistry

Question #555

Share Report

Which of the following is an endothermic reaction?

A. Burning of natural gas

B. Respiration

C. Reaction of sodium with water

D. Decomposition of calcium carbonate

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Endothermic reactions absorb heat from the surroundings. The decomposition of calcium carbonate (CaCO₃ → CaO + CO₂) requires continuous heating to proceed. Burning of gas, respiration, and the reaction of sodium with water are all exothermic reactions that release significant amounts of heat energy to the surroundings.

This question belongs to: Science chemistry

Question #556

Share Report

Balance the chemical equation: a Fe + b H₂O → c Fe₃O₄ + d H₂. The values of a, b, c, and d are:

A. 1, 3, 4, 3

B. 4, 3, 1, 4

C. 3, 4, 1, 4

D. 3, 1, 4, 4

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
To balance the equation: Fe atoms: 3 on right, so a=3. O atoms: 4 on right, so b=4. H atoms: 4*2=8 on left, so d=4. The balanced equation is 3Fe + 4H₂O → Fe₃O₄ + 4H₂. Thus, a=3, b=4, c=1, d=4. This ensures the law of conservation of mass is obeyed.

This question belongs to: Science chemistry

Question #557

Share Report

Assertion (A): Silver chloride turns grey when kept in sunlight. Reason (R): Silver chloride undergoes a decomposition reaction by sunlight.

A. A is false but R is true.

B. Both A and R are true but R is NOT the correct explanation of A.

C. A is true but R is false.

D. Both A and R are true and R is the correct explanation of A.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
When exposed to sunlight, silver chloride (AgCl) undergoes photolytic decomposition to form silver metal (which is grey) and chlorine gas. The equation is 2AgCl(s) + sunlight → 2Ag(s) + Cl₂(g). Both statements are correct, and the decomposition reaction perfectly explains the color change observed.

This question belongs to: Science chemistry

Question #558

Share Report

Which of the following is a strong acid?

A. Acetic acid

B. Carbonic acid

C. Citric acid

D. Hydrochloric acid

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Hydrochloric acid (HCl) is a strong acid because it completely dissociates into H⁺ and Cl⁻ ions in aqueous solution. Acetic, citric, and carbonic acids are weak acids as they only partially dissociate in water, establishing an equilibrium between the unionized molecules and their ions.

This question belongs to: Science chemistry

Question #559

Share Report

Baking soda is chemically:

A. Calcium carbonate

B. Sodium carbonate

C. Sodium hydroxide

D. Sodium bicarbonate

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Baking soda is sodium bicarbonate, with the chemical formula NaHCO₃. Sodium carbonate is washing soda (Na₂CO₃). Sodium hydroxide is caustic soda (NaOH), and calcium carbonate is limestone or marble (CaCO₃). Baking soda is widely used in baking as a leavening agent.

This question belongs to: Science chemistry

Question #560

Share Report

When a solution turns red litmus blue, its pH is likely to be:

A. 4

B. 1

C. 7

D. 10

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Red litmus turning blue indicates that the solution is basic. Basic solutions have a pH greater than 7. Among the options, 10 is the only value greater than 7. pH 1 and 4 are acidic (turn blue litmus red), and 7 is neutral (no change in litmus color).

This question belongs to: Science chemistry

Practice Questions

More Science Topics