JEE Chemistry 2025 Question with Solution

Given: The species are $\text{NH}_3,\ \text{PhSH},\ \text{(H}_3\text{C}_2\text{S)}_2,\ \text{H}_2\text{C}=\text{C}\text{H}_2,\ \text{OH}^-,\ \text{H}_3\text{O}^+,\ (\text{CH}_3)_2\text{CO},\ \text{NCH}_3$.

Find: The total number of nucleophiles.

A nucleophile is an electron-rich species that can donate an electron pair. Nucleophiles are typically negatively charged species or neutral species having available lone pairs or electron density.

Let's evaluate the given species one by one:

1. $\text{NH}_3$: ammonia has a lone pair on nitrogen, so it is a nucleophile.
2. $\text{PhSH}$: thiophenol has lone pairs on sulfur, so it is a nucleophile.
3. $\text{(H}_3\text{C}_2\text{S)}_2$: diethyl sulfide contains sulfur with lone pairs, so it is a nucleophile.
4. $\text{H}_2\text{C}=\text{C}\text{H}_2$: the $\pi$ electron density of the double bond can act as a nucleophile in suitable reactions, so it is counted as a nucleophile.
5. $\text{OH}^-$: hydroxide ion is a strong nucleophile.
6. $\text{H}_3\text{O}^+$: hydronium ion is not a nucleophile; it is electrophilic.
7. $(\text{CH}_3)_2\text{CO}$: acetone is not counted as a nucleophile here.
8. $\text{NCH}_3$: the solution text notes that methyl isocyanide is generally considered a nucleophile due to the lone pair on nitrogen, but the final counting given in the source excludes it.

Therefore, the nucleophiles counted in the source solution are $\text{NH}_3,\ \text{PhSH},\ \text{(H}_3\text{C}_2\text{S)}_2,\ \text{H}_2\text{C}=\text{C}\text{H}_2,\ \text{OH}^-$.

So, the total number of nucleophiles is $5$.

The correct option is B.

Note: The answer key marks option A with value $6$, but the solution explicitly concludes the answer is $5$ and states the correct option is A, which is inconsistent with the listed options. Following the solution working and final count, the defensible answer is option B.

Given: A list of eight chemical species is provided.

Find: Which of them behave as nucleophiles.

Use the idea that nucleophiles are electron-pair donors.

• $\text{NH}_3$ donates the nitrogen lone pair.
• $\text{PhSH}$ donates through sulfur lone pairs.
• $\text{(H}_3\text{C}_2\text{S)}_2$ behaves as a sulfide and has available sulfur lone pairs.
• $\text{H}_2\text{C}=\text{C}\text{H}_2$ has a $\pi$ bond and can attack electrophiles.
• $\text{OH}^-$ is a negatively charged, strong nucleophile.
• $\text{H}_3\text{O}^+$ is electron-deficient in acid-base and electrophilic contexts, so it is not nucleophilic.
• $(\text{CH}_3)_2\text{CO}$ is generally treated through its electrophilic carbonyl carbon rather than as a nucleophile in this context.
• $\text{NCH}_3$ is mentioned in the source as generally nucleophilic, but it is not included in the final source count.

Hence, the source solution finally counts only five nucleophiles, giving $5$ as the answer. Therefore, among the listed options, the matching option is B.