Ncert Exercises & Solutions

Select the correct option based on statements below:

Assertion (A):	HI cannot be prepared by the reaction of KI with concentrated H₂SO₄.
Reason (R):	HI has the lowest H—X bond strength among halogen acids.

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.

HINT: H₂SO₄ is a strong oxidising agent

Explanation:

STEP 1: HI cannot be prepared by the reaction of KI with concentrated H₂SO₄ because H₂SO₄ is a strong oxidising agent and it oxidised I^- into I₂ .

The reaction will be:

2 KI + H_{2} {SO}_{4} \to K_{2} {SO}_{4} + I_{2} + H_{2} S + H_{2} O

STEP 2: In the case of hydrogen halides (HX), The stability of these halides decreases down the group due to a decrease in bond

(H–X) dissociation enthalpy. Thus, HI has the lowest H—X bond strength among halogen acids.

Here, both Assertion and Reason are correct statements, and Reason is not the correct explanation of the Assertion.