Question

For a first order reaction, the time taken for the initial concentration to become $1/4^{th}$, is 10 minutes. What will be the time required to reduce the initial concentration to 1/16 of the initial value?

• A. 10 min
• B. 20 min
• C. 30 min
• D. 40 min

Answer 1

The correct option is B 20 min

The time required to reduce the initial concentration to a factor 1/4 is 10 min.
So, half life of the reaction is $\left(t_{\frac{1}{2}}\right)$ = 5 min.
$\therefore$ The time required to reduce the initial concentration to a factor 1/16 i.e. 4 half lives is = $(5\times 4)$ min = 20 min.