The two surfaces of a concave lens, made of glass of refractive index $1.5 $ have the same radii of curvature R. It is now immersed in a medium of refractive index $1.75$ then the lens,

Question

(a) becomes a convergent lens of focal length $3.5\;R$ (b) becomes a convergent lens of focal length $3.0\;R$ (c) changes as a divergent lens of focal length $3.5 \;R$ (d) changes as a divergent lens of focal length $3.0\;R$