In the following reaction ${\mathrm{H}}_3\mathrm{C}-\mathrm{C}\equiv \mathrm{CH} \underset{873\mathrm{K}}{\overset{\text{ red hot iron tube }}{\to }}\mathrm{A}$ ,

the number of sigma $\left(\sigma \right)$ bonds present in the product A is

H₃C − C≡CH →_{873 K, red hot iron tube} A

Analysis:

Under the given conditions (873 K and a red hot iron tube), the terminal alkyne (H₃C − C≡CH) undergoes trimerization to form benzene (C₆H₆) as the product A.

Structure of Benzene (C₆H₆):

• Benzene has a cyclic structure with 6 carbon atoms and alternating double bonds (a delocalized π-electron system).
• Each carbon atom in benzene forms:
  • Two single bonds (σ bonds) with adjacent carbon atoms.
  • One single bond (σ bond) with a hydrogen atom.

Total Sigma (σ) Bonds in Benzene:

Carbon-Carbon single bonds (C-C): 6 bonds (one σ bond per bond in the benzene ring).
Carbon-Hydrogen single bonds (C-H): 6 bonds (one σ bond per C-H bond).

Thus, the total number of σ bonds in benzene is:

6 (C-C bonds) + 6 (C-H bonds) = 12 σ bonds.

Answer: Since A (benzene) has 12 σ bonds, none of the options provided (21, 9, 24, 18) are correct. Could you confirm the options? It seems there's a mismatch in the options or interpretation of the question.