(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.