The rate constant of the reaction, $\mathrm{A}\to \mathrm{B}\text{ is }0.6\times {10}^{-3}$ mole per second. If the concentration of A is 5 M then concentration of B after 20 min is

Key concept For a zero order reaction unit of rate constant is (mol L^-1 s^-1 ). Hence, we can easily calculate concentration of B after 20 min by the following formula,
 $\mathrm{X}=\mathrm{kt}=0.6\times {10}^{-3}\times 20\times 60=0.72\mathrm{M}$