Answer:
The answer is 7.8 kJ / mol.
Explanation:
Energy = (number of methyl group) (Gauche interactions)(3.8kJ/mol per interaction)
= (2)(2)(3.8 kJ / mol)
= 15.2 kJ / mol.
The energy = (number of methyl group) - ( energy of gauche interactions)
= (23 kJ/mol) - 15.2 kJ/mol
= 7.8 kJ / mol.