Gas molecules of mass m are confined in a cylinder of radius r and height l (with r>l) kept vertically in the earth's gravitational field. the average energy of

Gas molecules of mass m are confined in a cylinder of radius R and height L (with R>L) kept vertically in the Earth's gravitational field. The average energy of the gas at low temperatures (such that mgl>> k,T) is given by (a) Nk,T/2 (b) 3Nk,T/2 (c) 2Nk,1T (d) 5Nk,7/2