$\because \mu=\frac{\text { Real depth }}{\text { apparent depth }}$
where, $\mu$ reflective index of medium
$\Rightarrow $ Apparent depth $=\frac{\text { Real depth }}{\mu}$
But, $\mu \propto \frac{1}{\lambda} $
$\because \lambda_{v} < \lambda_{g} < \lambda_{y} < \lambda_{r}$
Thus, $\mu_{v}$ is greater to all of them
$\therefore $ Apparent depth is minimum for violet.
It means that the violet letter appear raised more.
