dispersive power $w= \large\frac{\mu_v-\mu_{r}}{\mu -1}$

$\mu= \large\frac{\mu_v+\mu_r}{2}$

$\mu= \large\frac{1.522+1.514}{2}$

$\qquad= \large\frac{3.036}{2}$

$\qquad= 1.518$

$w= \large\frac{1.522 -1.514}{1.518-1}$

$\quad= \large\frac{0.008}{0.518}$

$\quad= 0.01554$

Hence a is the correct answer