Where should the object be placed to obtain a real and diminished image using a concave mirror?

$A$ ray of light $XY$ is incident on a spherical mirror as shown in the diagram. Redraw the diagram and mark the normal,angle of incidence and angle of reflection.

$A$ ray of light is incident normally on a reflecting surface. What are the $(i)$ angle of incidence and $(ii)$ angle of reflection?

The refractive indices of medium $(1)$ and medium $(2)$ are $\eta_{1}$ and $\eta_{2}$ respectively,and the velocities of light in these media are $v_{1}$ and $v_{2}$ respectively. What is the formula to find the refractive index of medium $(2)$ with respect to medium $(1)$,denoted as $\eta_{21}$?

The image formed by a convex mirror is only one-third of the size of the object. If the focal length of the mirror is $12 \, cm$,the image formed will be

What is the power of a concave lens of focal length $25\, cm$?