JEE Chemistry 2026 Question with Solution

Step-by-step solution

Common mistakes

• Assuming the entire mass of acetic anhydride is added for each hydroxyl group is incorrect because acetylation replaces the hydrogen of $-OH$, so the net mass increase per hydroxyl group is $42\,\text{g mol}^{-1}$. Use the net increase, not the reagent molar mass.

• Using the original molar mass $122\,g mol^{-1}$ directly to count hydroxyl groups is wrong because the number of hydroxyl groups depends on the increase in molar mass after acetylation. First calculate $290 - 122$.

• Choosing the option from the answer key without verifying the calculation can be risky. Always compute $\Delta M$ and divide by $42$ to confirm the number of hydroxyl groups.