JEE Chemistry 2025 Question with Solution

Step-by-step solution

Standard Method

Given: Four reactions of benzenediazonium chloride are shown.

Find: Which reaction is not correct.

Recognize the reactions involved: Sandmeyer reaction, hydrolysis, and nucleophilic substitution.

Benzenediazonium chloride does not give ethoxybenzene with ethanol. Ethanol acts as a reducing agent and the diazonium group is replaced by hydrogen, giving benzene. Therefore the reaction shown in option A is not correct.

The other reactions are valid:

• with phosphoric acid and water, the diazonium salt can lead to deamination product benzene under the shown context,
• with potassium iodide, iodobenzene is formed,
• with $\text{CuCN}/\text{KCN}$, benzonitrile is formed.

Therefore, the correct option is A.

Common mistakes

• Assuming ethanol behaves as a nucleophile to give ethoxybenzene directly is incorrect. In reactions of arenediazonium salts, ethanol commonly acts as a reducing agent. Instead, remember that the diazonium group is often replaced by hydrogen in the presence of ethanol.

• Confusing all diazonium substitutions as Sandmeyer reactions is incorrect. Only certain substitutions use copper salts such as $\text{CuCN}$ or $\text{CuCl}$. Check the reagent carefully before assigning the product.

• Mistaking potassium iodide substitution for an invalid reaction is wrong because iodide ion readily replaces the diazonium group to form iodobenzene. Verify whether the reagent is a known diazonium replacement reagent before rejecting the option.