Enthalpy change via bond energies Steps:

• Bonds broken: H-H (436 kJ/mol) and Br-Br (193 kJ/mol); total input = 436 + 193 = 629 kJ/mol.
• Bonds formed: 2 H-Br (366 kJ/mol each); total output = 2 × 366 = 732 kJ/mol.
• ΔH = energy to break bonds - energy from forming bonds = 629 - 732 = -103 kJ/mol. Why B is correct:
• Matches ΔH formula: endothermic bond breaking minus exothermic bond forming yields negative value for exothermic reaction. Why the others are wrong:
• A: Wrong sign; ignores net energy release.
• C: Wrong sign; calculation shows energy release, not absorption.
• D: Only H-H energy; ignores Br-Br and H-Br contributions.

Final answer: B