See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Huckel's rule states that a planar, cyclic, fully conjugated system is aromatic if it contains (4n + 2) pi electrons, where n is a non-negative integer (0, 1, 2, ...). Step 1: Identify the base compound. All options are cyclobutadiene-based (C4H4) ring systems, which is a 4-membered fully conjugated cyclic system. Step 2: Count pi electrons in neutral C4H4 (cyclobutadiene). Cyclobutadiene has 4 pi electrons (4n system, n=1), which is anti-aromatic. Step 3: Evaluate each option: - (a) C4H4^(-1): Adding 1 electron to the 4 pi electrons gives 5 pi electrons. 5 does not fit 4n+2 for any integer n. Not aromatic. - (b) C4H4^(+1): Removing 1 electron from 4 pi electrons gives 3 pi electrons. 3 does not fit 4n+2 for any integer n. Not aromatic. - (c) C4H4^(-2): Adding 2 electrons to the 4 pi electrons gives 6 pi electrons. 6 = 4(1) + 2, so n=1. This satisfies Huckel's rule. The cyclobutadiene dianion is aromatic. - (d) C4H4: 4 pi electrons. 4 = 4n (n=1), anti-aromatic. Does not obey Huckel's rule. Step 4: Only C4H4^(-2) with 6 pi electrons satisfies the 4n+2 rule, making it aromatic according to Huckel's rule. Therefore, the correct answer is C.