The molar heat of fusion of gold is 12.550 kj mol–1. at its melting point, how much mass of melted gold must solidify to release 235.0 kj of energy?

The total heat released, Q, equals number of moles, n, times molar heat of fussion, Hf. this is: Q = n * Hf. You kno Q and Hf, so you can find n as n = Q/Hf = 235.0 kJ / 12.55 kJ/mol = 18.72 mol. Now you can pass that to mass using the atomic mass of Au, which is 197 g/mol => mass = 18.73 mol * 197 g/mol = 3688.9 grams.