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In the following reaction, H3C−C≡CH (Red hot iron tube, 873 K) → A, the number of sigma (σ) bonds present in the product A, is

1. 18
2. 21
3. 9
4. 24

Correct answer: 21

Solution

When propyne (H3C−C≡CH) is passed through a red-hot iron tube at 873 K, it undergoes trimerization to form benzene (C6H6). Benzene has 12 sigma bonds from C-H and C-C single bonds, and 9 sigma bonds from the C=C bonds, totaling 21 sigma bonds.

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