Light travels along a straight line. The fact that light travels in a straight path can be demonstrated by putting an object in its path. If the object is opaque and casts a dark shadow then, it shows that light travels in a straight line.

Answer : 1 Mark
Yes, light is necessary to see objects. If there is no light then there will be no reflection from an object and no light will reach our eye and we will not be able to see any object.

Explanation: 2 Marks
If the letters of English alphabet A, H, I, M, O, T, U, V, W, X, Y are kept in front of a plane mirror, then they would form images which exactly look like the original letters of the alphabet. These letters are vertically symmetric. For example, if we divide letters A and U in the middle, then we would find that the right halves are equivalent to the left halves of the letters.

Hence, even if the image interchanges sidewise, it will appear same as the letter.

Answer : 1 Mark
Reason : 1 Mark
A concave lens always forms a virtual image of an object.
A concave lens is also called a diverging lens and hence, the light particles never actually meet. But when they are produced backwards, they form a virtual image.

Answer : 1 Mark
Reason : 1 Mark
Convex mirror is used as reflectors at sharp turns or blind corners.
Convex mirrors are also known as converging mirror. Because of this the image formed by the mirror is a converged image of numerous objects. This gives the driver a larger field of vision thus, helping them take well-informed decisions.

(a) Answer: 1.5 Marks
(b) Answer with explanation: 1.5 Marks
(a) A mirror image formed by a plane mirror is identical in size and shape but is laterally inverted.
If we move our right hand to the right, our image will move the left hand towards the left. It is because in a plane mirror our "left appears right” and "right appears left”. This is called a lateral inversion.  
(b) According to the law of reflection, the angle of incidence is equal to the angle of reflection. If the reflected ray is at an angle of ${90}^{\circ }$ to the incident ray, it implies that the reflected ray will be making an angle of ${45}^{\circ }$ from the normal. Hence, the angle of reflection is ${45}^{\circ }$, therefore the angle of incidence of the ray is ${45}^{\circ }$ according to the law of reflection. 

(a) Definition: 1 Mark
(b) Explanation: 2 Marks
(a) The image that cannot be obtained on a screen is called a virtual image.
(b) A virtual image is an image formed when the outgoing rays from a point on an object always diverge. The image appears to be located at the point of apparent divergence. Because the rays never really converge, a virtual image cannot be projected onto a screen.

Characteristics : 3 Marks
Any 3:
The image formed by a plane mirror is:

1) Erect

2) Of the same size as of the object

3) Appears to be at the same distance from the mirror as the object is in front of it

4) Virtual

5) Laterally inverted