(a) 'Refraction of light' is responsible for this property. [1 mark]
(b) When light coming from denser medium enters the rarer medium, it is bent away from the normal.
Let any object B is at the bottom of a pond. Consider a light ray BC from the object that moves from water to air. After refraction from the water surface, the ray moves away from the normal N along the path CD. The produce of CD appears from the point B' and a virtual image of the object at B appears at B'.
The pond appears to be three-quarters of its actual depth due to the property of refraction of light.
Refractive index μ=Real depthApparent depth
Since μ=43 for water
Therefore, Apparent depth = 43× Real depth [2 marks]