Question

Two ideal di-atomic gases A and B. A is rigid, B has an extra degree of freedom due to vibration. Mass of A is m and mass of B is m/4. The ratio of molar specific heat of A to B at constant volume is : 

(1) 7/9

(2) 5/9

(3) 5/11

4) 5/7

Answer 1

The answer is (4) 5/7 

Molar heat capacity of A at constant volume = 5R/2

Molar heat capacity of B at constant volume = 7R/2

Dividing both,(C_v)A/(C_v)B = 5/7.