The ray of light which is sent back by the reflecting surface is called a reflected ray. Normal line: The perpendicular line drawn on to the surface of the mirror at the point of incidence is called normal line.

Explanation:

When a light ray strikes a surface, it can be absorbed, transmitted or reflected. The angle of incidence is the angle between the incident ray and the normal and the angle of reflection is the angle between the reflected ray and the normal. The normal is an imaginary line drawn perpendicular to the surface at the point of incidence.

The correct answer is option 'D' because the line drawn perpendicular to the reflecting surface at the point of incidence is called the normal. The normal is an important concept in optics because it helps us to understand how light rays behave when they strike a surface. When a light ray strikes a surface at an angle, it is reflected at the same angle on the other side of the normal.

The normal is important because it helps us to understand how light rays are reflected. When a light ray strikes a surface at an angle, it is reflected at the same angle on the other side of the normal. This is known as the law of reflection. The normal is also important because it helps us to determine the angle of incidence and the angle of reflection.

Summary:

- The line drawn perpendicular to the reflecting surface at the point of incidence is called the normal.
- The normal is an imaginary line that helps us to understand how light rays are reflected.
- The normal is important because it helps us to determine the angle of incidence and the angle of reflection.

Normal is the line from which the incident ray is reflected at a particular angle which is called the reflected ray.