When silvered on the convex side the Plano convex lens behaves like a concave mirror of focal length 10 cm. R is the radius of curvature cm. Hence, the correct answer is option (D).

Which side is silvered of concave mirror?

concave mirrors are silvered from the inside portion of the sphere .

What is the convex side of a lens?

Most lenses are spherical lenses: their two surfaces are parts of the surfaces of spheres. Each surface can be convex (bulging outwards from the lens), concave (depressed into the lens), or planar (flat). The line joining the centres of the spheres making up the lens surfaces is called the axis of the lens.