Question

a hollow sphere floats with entire volume in water at 4°C sinks when water is heated above 4°C

Answer 1

As we know when water is heated from 0 to 4 degrees, it expands. From 0 to 4 degrees, it contracts instead of expanding and at 4 degree it starts expanding. so its density also increases and the volume is decreased. This makes the sphere to float. but above this temperature, the sphere descends 

Answer 2

Explanation:

A plane paper reflect only white colour (if nothing is written)butplane mirror reflects every colour to form image. Surface, Ray oflight which strikes through it reflect at as same angle of incidence. But plane sheet of paper is rough so Ray of light striking through it will get distorted after reflection.