Block B will come to rest, if force applied to it will vanish due to frictional force acting between block B and surface, i.e, foce applied = frictional force

i.e., $\mu \mathrm{mg}=\mathrm{ma}$ or $\mu \mathrm{mg}=\mathrm{m}\left(\frac{\mathrm{v}}{\mathrm{t}}\right)$

or $\quad \mathrm{t}=\frac{\mathrm{v}}{\mu \mathrm{g}}$

So, The correct option of this question is **(A).**