A body is said to be opaque to the radiation if (a, r and t are coefficient of absorption, reflection and transmission respectively)

In a thermodynamic system, $$\Delta U$$ represents the increases in its internal energy and dW is the work done by the system then correct statement out of the following is

The temperature of a gas is $$-68^{\circ} \mathrm{C}$$. To what temperature should it be heated, so that the r.m.s. velocity of the molecules be doubled?

A sphere, a cube and a thin circular plate all made of same material and having the same mass are heated to same temperature of $$200^{\circ} \mathrm{C}$$. When these are left in a room.