The correct order of molar heat capacities measured at 298 K and 1 bar is :

Step-by-step solution

The molar heat capacity of Helium (a monatomic gas) at constant pressure is C_p = 5 2 R 20.8 J K ⁻¹ mol ⁻¹ . The molar heat capacity of Copper (a solid) follows the Dulong-Petit law, which gives C_p 3R 24.9 J K ⁻¹ mol ⁻¹ . The molar heat capacity of Bromine (a diatomic liquid) is significantly higher due to translational, rotational, and vibrational degrees of freedom along with intermolecular interactions in the liquid state, having C_p 75.7 J K ⁻¹ mol ⁻¹ . Therefore, the correct order of molar heat capacities is