If time required for 90 % completion of a first order reaction is 't'. What is the time required for 99.9 % completion of reaction at same temperature?

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Correct answer: A. 3t

For a first order reaction, the time required for completion is given by t = 2.303 k ( a a-x ) For 90\% completion, x = 0.9a t_ 90\% = 2.303 k ( a a - 0.9a ) = 2.303 k 10 = 2.303 k Given t_ 90\% = t, so t = 2.303 k For 99.9\% completion, x = 0.999a t_ 99.9\% = 2.303 k ( a a - 0.999a ) = 2.303 k 1000 = 2.303 k 3 Substituting the value of t, we get t_ 99.9\% = 3t Answer: 3t

MHT CET Chemistry Question (2026) — Solution

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