Answer
$1.97\times 10^{8}$ $m/s$
Work Step by Step
If $c^\prime$ be the speed of light in a medium, then the refractive index $(n_r)$ of that medium can defined as
$n_r=\frac{c}{c^\prime}$
where, $c$ is the speed of light in vacuum
The the refractive index of benzene is given:
$n_r=1.52$
$\therefore$ The speed of light in benzene is given by
$c^\prime=\frac{c}{n_r}$
or, $c^\prime=\frac{3\times 10^8}{1.52}$ $m/s$
or, $c^\prime\approx 1.97\times 10^{8}$ $m/s$
