Two cylinders A and B fitted with pistons contain equal amounts of an ideal diatomic gas at 300 K. The piston of A is free to move while that of B is held fixed. The same amount of heat is given to the gas in each cylinder. If the rise in temperature of the gas in A is 30 k, then the rise in temperature of the gas in B is : 

42 K

For A : As piston is free to move, the process is isobaric.

\(\Delta Q = \mu C_P \Delta T_1\)

For B : As piston is held fixed, the process is isochoric.

\(\Delta Q = \mu C_V \Delta T_2\)

Now : \(C_P \Delta T_1 = C_P \Delta T_2\)

\(\frac{7}{2}R*30 = \frac{5}{2}R* \Delta T_2\)

\(\Delta T_2 = 42 K\)