in which of the following gas, vibrational mode is excited at room temperature

chlorine

hydrogen

oxygen

nitrogen

Note that the diatomic gas does not have a heat capacity of 72R as you would expect if rotation about its axis or vibration along its axis were involved in storing energy. The reason is that these modes are quantized - and that the thermal energies are insufficient to excite a reasonable fraction of the molecules into the higher energy state. Thus the assumptions that go into the equipartition principle don't apply - and the heat capacity reflects that.