Explain how a fish deep inside a pond full of water can see everything above the water near the pond. Show that the field of vision of the fish is concentrated within a cone of apex angle `98^@`.

Bharath went to his grandfather’s house in winter this year. As usual he went for fishing. His grandmother told him there will be no fishes in the lake. He noticed that it was more difficult to find fishes in winter. The fishes were deep inside the river. Whereas in summer they were on the surface and hence he was able to catch fishes. (a) Why are fishes on the surface in water than in the depth in summer? Srisha wanted to keep ice creams without melting. So he had to keep it on ice taken in a container. His grandmother advised him to pour salt on the ice. (a) Why? (b) What value can be derived from this?