JEE Chemistry 2025 Question with Solution

Given: The compound has molecular formula $\mathrm{C_6H_6}$, gives only one monobromo derivative, and shows aromatic character consistent with benzene.

Find: The number of $\pi$ electrons.

The compound with molecular formula $\mathrm{C_6H_6}$ is benzene. Benzene has a cyclic conjugated structure with three double bonds represented in its resonance forms.

Each double bond contributes $2$ $\pi$ electrons.

The fact that it gives only one monobromo derivative shows that all six hydrogen atoms are equivalent, which supports the benzene structure.

Therefore, the number of $\pi$ electrons is $6$.

Given: An aromatic compound with formula $\mathrm{C_6H_6}$ that gives only one monobromo derivative.

Find: The number of $\pi$ electrons.

Aromatic compounds follow Hückel's rule:

For benzene,

which corresponds to $n = 1$. Hence benzene contains $6$ $\pi$ electrons.

Therefore, the required numerical answer is $6$.