Which of the following statements is true regarding a real image of an object?

$(a)$ $A$ ray of light falls normally on a face of a glass slab. What are the values of angle of incidence and angle of refraction of this ray?
$(b)$ Light enters from air to a medium $X$. Its speed in medium $X$ becomes $1.5 \times 10^{8} \ m \ s^{-1}$. Speed of light in air is $3 \times 10^{8} \ m \ s^{-1}$. Find the refractive index of medium $X$.

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 happens when an oblique ray of light enters from glass into air?

What is the centre of a curved mirror called?

Under what condition in an arrangement of two plane mirrors,will the incident ray and the final reflected ray always be parallel to each other,regardless of the angle of incidence? Show the same with the help of a diagram.