The reaction 2 X → B is a zeroth order reaction.

The reaction $2 X \rightarrow B$ is a zeroth order reaction. If the initial concentration of $\mathrm{X}$ is $0.2 \mathrm{M}$, the half-life is $6 \mathrm{~h}$. When the initial concentration of $\mathrm{X}$ is $0.5 \mathrm{M}$, the time required to reach its final concentration of $0.2 \mathrm{M}$ will be :-