JEE Chemistry 2025 Question with Solution

Given: Two statements about the reactions of propyne with sodium and $\mathrm{NaNH_2}$ are to be checked.

Find: Which statement is correct.

For Statement I, propyne is a terminal alkyne and contains one acidic hydrogen atom. It reacts with sodium as:

$$\mathrm{C_3H_3-H + Na \rightarrow C_3H_3Na + \frac{1}{2}H_2}$$

So, one mole of propyne liberates half a mole of $\mathrm{H_2}$ gas. Therefore, Statement I is correct.

For Statement II, molar mass of propyne $\mathrm{(C_3H_4)}$ is:

$$3 \times 12 + 4 \times 1 = 40 \, \text{g mol}^{-1}$$

Hence, moles of propyne in $4 \, \text{g}$ are:

$$\frac{4}{40} = 0.1 \, \text{mol}$$

Reaction with $\mathrm{NaNH_2}$ is:

$$\mathrm{C_3H_4 + NaNH_2 \rightarrow C_3H_3Na + NH_3}$$

Thus, $0.1 \, \text{mol}$ propyne gives $0.1 \, \text{mol}$ $\mathrm{NH_3}$.

At STP, $1 \, \text{mol}$ gas occupies $22.4 \, \text{L}$. Therefore, volume of $0.1 \, \text{mol}$ $\mathrm{NH_3}$ is:

$$0.1 \times 22.4 = 2.24 \, \text{L}$$

This is $2240 \, \text{mL}$, not $224 \, \text{mL}$. Therefore, Statement II is incorrect.

Hence, the correct option is A.

Given: Two independent statements are provided.

Find: Truth value of each statement.

1. Statement I depends on the acidic hydrogen of a terminal alkyne. One hydrogen atom from two molecules combines to form one molecule of $\mathrm{H_2}$, so per mole of propyne the amount of hydrogen released is:

$$\frac{1}{2} \, \text{mol of } \mathrm{H_2}$$

Hence, Statement I is true.

2. Statement II requires stoichiometry and gas volume calculation.

Mass of propyne = $4 \, \text{g}$

$$\text{Moles of propyne} = \frac{4}{40} = 0.1$$

From the reaction:

$$\mathrm{C_3H_4 + NaNH_2 \rightarrow C_3H_3Na + NH_3}$$

Mole ratio of propyne to $\mathrm{NH_3}$ is $1:1$, so moles of $\mathrm{NH_3}$ formed = $0.1 \, \text{mol}$.

Now,

$$\text{Volume at STP} = 0.1 \times 22.4 = 2.24 \, \text{L}$$

Given statement says $224 \, \text{mL}$, which is incorrect.

Therefore, Statement I is correct but Statement II is incorrect, so the correct option is A.