CASE STUDY: MIRAGE IN DESERTS

To a distant observer, the light appears to be coming from somewhere below the ground. The observer naturally assumes that light is being reflected from the ground, say, by a pool of water near the tall object.
Such inverted images of distant tall objects cause an optical illusion to the observer. This phenomenon is called mirage. This type of mirage is especially common in hot deserts. Based on the above facts, answer the following questions:

(a) Which of the following phenomena is prominently involved in the formation of mirage in deserts?
(b) A driver at a depth 12m inside water sees the sky in a cone of semi vertical angle ?
(c) In an optical fibre, if `n_1` and `n_2` are refractive indices of the core and cladding, then which among the following would be a correct equation?
(d) A diamond is immersed in such a liquid which has its refractive index with respect to air as greater than the refractive index of water with respect to air. Then the critical angle of diamond liquid interface as compared to critical angle of diamond water interface will?