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Chloroform (CHCl3) reacts with silver metal upon heating: 2CHCl3 + 6Ag -> P. P is then passed through a hot iron tube to give Q. What are P and Q, and what is the degree of unsaturation of Q?

1. P is ethyne and Q is benzene, degree of unsaturation = 4
2. P is ethene and Q is benzene, degree of unsaturation = 4
3. P is ethyne and Q is cyclohexane, degree of unsaturation = 1
4. P is acetylene and Q is benzene, degree of unsaturation = 4

Correct answer: P is ethyne and Q is benzene, degree of unsaturation = 4

Solution

Two CHCl3 molecules react with 6 Ag to give ethyne (CH≡CH) as P, with AgCl as byproduct. Ethyne on passing through a hot iron tube undergoes trimerisation to give benzene (Q). Degree of unsaturation of benzene = 4.

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