(b) Hydrogen gas at 1 standard atm. and 25 C flows through a pipe made of unvulcanised neoprene rubber with ID and OD of 25 and 50 mm respectively. If the concentration of hydrogen at the inner surface of the pipe is 2.37x10 kmol hydrogen/m and the diffusivity of hydrogen gas through the rubber is 1.8x106 cms, estimate the rate of loss of hydrogen by diffusion through a pipe of 2 m length. The outer air may be assumed to be free from hydrogen