The refractive index of the material of a concave lens is $\mu$  and is placed in the medium of refractive index ${\mu }^1$ . If ${\mu }^1<\mu$ the following ray diagram is correct

Focal length of a lens is given by:-

$\frac{1}{f}=(n-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$   where  $n=\frac{\mu }{{\mu }^{{}^{\prime }}}$

Since, here, $n=\frac{\mu }{{\mu }^{{}^{\prime }}}>1$ and by convention $R_1$ is negative and $R_2$ is positive

Hence, $f$ comes out to be negative.

Thus, this system will behave as a $Concave$ $lens$ though with larger focal length than in air.

Hence,option-(B) is correct.