Silvering of Lens

When a thin plano-convex lens $(\mu =1.5)$ polished from its plane surface behave like a concave mirror of focal length $40 \mathrm{cm}$. The radius of curvature of the lens is

A concave lens of radius of curvature $15 \mathrm{cm}$ and $\mu =1.5$ is placed in water $\left(\mu =\frac{4}{3}\right).$ If one surface is silvered, then image distance from lens when an object is placed at distance of $14 \mathrm{cm}$ from the lens is

An object is placed $1.5 \mathrm{m}$ in front of the curved surface of a planoconvex lens whose flat surface is silvered. A real image is formed $300 \mathrm{cm}$ in front of the lens. The focal length of the lens is

A point object $O$ is placed at a distance of $30 \mathrm{cm}$ from a convex lens of focal length $20 \mathrm{cm},$ cut into two halves each of which is displaced by $5\times {10}^{-2} \mathrm{cm}$ as shown. Choose the correct option(s).