The standard enthalpy change of formation Hf is the enthalpy change when one mole of a compound is formed from its elements in their standard states. In this case, we want to find the Hf for MgO s using the given data.The reaction for the formation of MgO from its elements in their standard states is:Mg s + 1/2 O g MgO s The standard enthalpy change of formation Hf for this reaction can be calculated using Hess's Law, which states that the enthalpy change of a reaction is the sum of the enthalpy changes of the individual steps. In this case, we have:Hf [MgO s ] = Hc [MgO s ] - Hf [Mg s ] - 1/2 Hf [O g ]Since Hf for Mg s and O g are both 0 kJ/mol, the equation simplifies to:Hf [MgO s ] = Hc [MgO s ]So, the standard enthalpy change of formation of magnesium oxide MgO is:Hf [MgO s ] = -601.8 kJ/mol