At STP, the molar heat capacity of oxygen gas is nearly 2.5 R . With an increase in temperature, it gradually rises and approaches 3.5 R . The most fitting reason for this behaviour is that at high temperatures

Step-by-step solution

At STP, oxygen ( O₂ ) acts as a rigid diatomic molecule with 3 translational and 2 rotational degrees of freedom. Total degrees of freedom, f = 5 . The molar heat capacity at constant volume is C_v = f 2 R = 5 2 R = 2.5 R . At high temperatures, the vibrational degrees of freedom become active. A diatomic molecule has one vibrational mode, which contributes 2 additional degrees of freedom (one for kinetic energy and one for potential energy). Total degrees of freedom at high temperature, f = 5 + 2 = 7 . The molar h