Question

Concentration of the reactant in first order is reduced to ${\frac{1}{e}}^2$ after

• A. one natural life time
• B. two natural life time
• C. three natural life time
• D. four natural life time

Answer 1

The correct option is B two natural life time

Natural life time = $\frac{1}{K}$
$\left[C\right]=\left[C_0\right]e^{–Kt}\frac{\left[C\right]}{e^2}=\left[C_0\right]e^{(}-Kt)e^{(}-2)=e^{(}-kt)Kt=2t=\frac{2}{K}$