Question

For a first order reaction, the time taken to reduce the initial concentration by a factor of 1/4 is 20 min. The time required to reduce initial concentration by a factor of 1/16 is

• A. 20 min
• B. 10 min
• C. 80 min
• D. 40 min

Answer 1

Answer: (D)

40 min

Answer 2

$1 \xrightarrow {1} \frac{1}{2} \, \xrightarrow {2} \, \frac{1}{4} \, \xrightarrow {3} \frac{1}{8} \xrightarrow {4} \frac{1}{16}$
$\frac{1}{16}$ is 4 half-lives and $\frac{1}{4}$ is 2 half-lives.