Which value would be required to estimate the lattice energy for the hypothetical ionic compound MgH2?

A the electron affinity

B the first ionisation energy

C the magnesium-hydrogen bond energy

D the standard enthalpy change of formation of MgH2

D, the energy of formation is equal to the dissociation. so from magnesium ions and Hydrogen ions, when they form the lattice energy is equal to formation-dissociation, as they aren't going to dissociate (fixed in lattice) the formation should be the same as the the overall lattice energy.