Assertion (A): Chlorine can displace iodide ions from KI solution.

Reason (R): It is an example of displacement reaction.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Assertion (A): Silver is displaced by copper from the aqueous solution of silver nitrate.

Reason (R): Copper is placed below silver in the activity series.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Riya was revising different types of chemical reactions studied in class. She recalled that:

$\bullet$ A double displacement reaction generally takes place in an aqueous solution where the ions of two compounds exchange places.

$\bullet$ If one of the products formed is an insoluble solid, the reaction is called a precipitation reaction.

$\bullet$ A reaction in which an acid or acidic oxide reacts with a base or basic oxide to form salt and water is known as a neutralisation reaction.

To understand these reactions better, Riya observed the following experiments.

(a) When hydrogen sulphide gas (H₂S) was passed through a blue solution of copper sulphate, a black solid was formed along with sulphuric acid.

(i) Identify the type of reaction taking place.
(ii) Name the black solid formed.

(b) Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.
Explain why this reaction is considered a double displacement reaction.

(c) Complete and balance the following chemical equation ;

Pb(NO₃)₂ (aq.) + KI ⟶ …… + ……

(d) State one observable change that indicates the reaction in part (c) has taken place.

A water insoluble substance A on reacting with dilute H₂SO₄ releases a gas which turns a paper dipped in acidified potassium dichromate solution green. When the gas is passed through lime water, the solution obtained turns blue litmus red. On bubbling the gas through lime water, it initially became turbid and the turbid nature disappeared when the gas is passed in excess.

(a) Identify the substance 'A'.

(b) Write the chemical equations of the reactions involved.

(c) State the type of reactions that are involved.