Chemical Reactions and Equations

2026MCQ·1 mark·Q17Combination and decomposition reactions

The volume ratio of hydrogen and oxygen gases liberated during electrolysis of water is

1. (a) 1 : 1
2. (b) 2 : 1
3. (c) 4 : 1
4. (d) 1 : 2

2026MCQ·1 mark·Q18Combination and decomposition reactions

C_6H_{12}O_6(aq) + 6O_2(g) -> 6CO_2(g) + 6H_2O(l). The above reaction is an example of -

1. (a) Displacement Reaction
2. (b) Endothermic Reaction
3. (c) Exothermic Reaction
4. (d) Neutralisation Reaction

2026Short answer·3 marks·Q26Combination and decomposition reactions

Account for the following: (a) White silver chloride turns grey when exposed to sunlight. (b) Lead (II) nitrate on heating releases brown fumes. (c) Bags of oil and fat containing food items are flushed with nitrogen gas.

2025Very short answer·2 marks·Q21Chemical equations and how to write them

A student performs the following experiment in his school laboratory (a conical flask fitted with a delivery tube containing dilute sulphuric acid and Zn granules - see figure). List two observations to justify that in this experiment a chemical change has taken place.

2025MCQ·1 mark·Q1Combination and decomposition reactions

Electrolysis of water is a decomposition reaction. The mass ratio (M_H : M_O) of hydrogen and oxygen gases liberated at the electrodes during electrolysis of water is :

1. (a) 8 : 1
2. (b) 2 : 1
3. (c) 1 : 2
4. (d) 1 : 8

2025Assertion-Reason·1 mark·Q17Combination and decomposition reactions

Assertion (A): Decomposition reactions are generally endothermic reactions. Reason (R): Decomposition of organic matter into compost is an exothermic process. Select the correct answer:

1. (a) Both A and R are true and R is the correct explanation of A.
2. (b) Both A and R are true, but R is not the correct explanation of A.
3. (c) A is true, but R is false.
4. (d) A is false, but R is true.

2024MCQ·1 mark·Q1Balancing a chemical equation

When 2 mL of sodium hydroxide solution is added to few pieces of granulated zinc in a test tube and then warmed, the reaction that occurs can be written in the form of a balanced chemical equation as:

1. (a) NaOH + Zn -> NaZnO_2 + H_2
2. (b) 2NaOH + Zn -> Na_2ZnO_2 + H_2
3. (c) 2NaOH + Zn -> NaZnO_2 + H_2
4. (d) 2NaOH + Zn -> Na_2ZnO_2 + H_2O

2024MCQ·1 mark·Q2Combination and decomposition reactions

Select from the following a decomposition reaction in which source of energy for decomposition is light:

1. (a) 2FeSO_4 -> Fe_2O_3 + SO_2 + SO_3
2. (b) 2H_2O -> 2H_2 + O_2
3. (c) 2AgBr -> 2Ag + Br_2
4. (d) CaCO_3 -> CaO + CO_2

2024Very short answer·2 marks·Q21Combination and decomposition reactions

Name the type of chemical reaction in which calcium oxide reacts with water. Justify your answer by giving balanced chemical equation for the chemical reaction.

2024Short answer·3 marks·Q27Combination and decomposition reactions

Write one chemical equation each for the chemical reaction in which the following have taken place: (i) Change in colour (ii) Change in temperature (iii) Formation of precipitate. Mention colour change/temperature change (rise/fall)/compound precipitated along with equation.

2024MCQ·1 mark·Q7Oxidation and reduction

MnO_2 + 4HCl -> MnCl_2 + 2H_2O + Cl_2. The reaction given above is a redox reaction because in this case:

1. (a) MnO_2 is oxidised and HCl is reduced.
2. (b) HCl is oxidised.
3. (c) MnO_2 is reduced.
4. (d) MnO_2 is reduced and HCl is oxidised.

2023Very short answer·2 marks·Q21(b)Chemical equations and how to write them

Write balanced chemical equation for the reaction that occurs when: (i) blue coloured copper sulphate crystals are heated and (ii) Sodium hydrogen carbonate is heated during cooking.

2023MCQ·1 mark·Q3Balancing a chemical equation

MnO_2 + x HCl -> MnCl_2 + y H_2O + z Cl_2. In order to balance the above chemical equation, the values of x, y and z respectively are:

1. (a) 6, 2, 2
2. (b) 4, 1, 2
3. (c) 4, 2, 1
4. (d) 2, 2, 1

2023MCQ·1 mark·Q2Combination and decomposition reactions

The emission of brown fumes in the given experimental set-up is due to

1. (a) thermal decomposition of lead nitrate which produces brown fumes of nitrogen dioxide.
2. (b) thermal decomposition of lead nitrate which produces brown fumes of lead oxide.
3. (c) oxidation of lead nitrate forming lead oxide and nitrogen dioxide.
4. (d) oxidation of lead nitrate forming lead oxide and oxygen. [Set-up shows lead nitrate being heated over a burner, giving off brown fumes.]

2023Short answer·3 marks·Q27Oxidation and reduction

(a) Identify the reducing agent in the following reactions: (i) 4NH_3 + 5O_2 -> 4NO + 6H_2O (ii) H_2O + F_2 -> HF + HOF (iii) Fe_2O_3 + 3CO -> 2Fe + 3CO_2 (iv) 2H_2 + O_2 -> 2H_2O. (b) Define a redox reaction in terms of gain or loss of oxygen.