Which type of spherical mirror has its reflecting surface curved inwards, facing towards the centre of the sphere?

The correct option is Concave mirror.

To understand why this is the correct answer, let us look at the definition and structure of spherical mirrors:

1. A spherical mirror is a mirror that has the shape of a piece cut out of a spherical surface.

2. There are two main types of spherical mirrors based on which side is the reflecting surface:
- Concave Mirror: A spherical mirror whose reflecting surface is curved inwards, facing towards the centre of the sphere. It is also known as a converging mirror because it converges the parallel rays of light falling on it.
- Convex Mirror: A spherical mirror whose reflecting surface is curved outwards, facing away from the centre of the sphere. It is also known as a diverging mirror.

3. Since the question asks for the spherical mirror that has its reflecting surface curved inwards and facing towards the centre of the sphere, it matches the definition of a Concave mirror.