A hollow double concave lens is made of very thin transparent material It can be filled with air or either of two liquids $L_1$ or $L_2$ having refracting indices $n_1$ and $n_2$ respectively $( n_2 > n_1 > 1)$ The lens will diverge a parallel beam of light if it is filled with

Question

(a) $L_2$ and immersed in $L_1$ (b)air and immersed in $L_1$ (c) $L_1$ and immersed in $L_2$ (d)air and placed on air