If the central portion of a convex lens is wrapped in black paper as shown in the figure.

In the figure, an air lens of radii of curvature $10 \mathrm{cm}\left(R_1=R_2=10 \mathrm{cm}\right)$ is cut in a cylinder of glass $(\mu =1.5).$ The focal length and the nature of the lens is

The correct conclusion that can be drawn from these figures is

The focal length of a convex lens made from a material of refractive index $1.52$ is $10 \mathrm{cm}$ when placed in air. If it is immersed in carbon disulphide of refractive index $1.68$, then its focal length and nature will be