Physics · THERMODYNAMICS

A solid consists of \( N \) atoms vibrating about their mean positions. Considering 3 independent vibrational degrees of freedom where each mode contributes an average energy of \( k_B T \) (potential + kinetic), the total internal energy for \( 2.5 \text{ moles} \) of this elemental solid is (where \( R \) is the universal gas constant):

1. A
   \( 7.5 RT \)
2. B
   \( 5.0 RT \)
3. C
   \( 2.5 RT \)
4. D
   \( 15.0 RT \)