Question

A first order reaction is 75% completed in 72 min. The time it will take for 50% completion is:

• A. 36 min
• B. 43 min
• C. 48 min
• D. 54 min

Answer 1

The correct option is A 36 min

For a first order reaction, the ratio $\frac{t_{0.75}}{t_{0.5}}=2$. It is independent of the initial concentration.

$t_{0.75}=72$ min. Hence, $t_{0.5}=\frac{72}{2}=36$ min.