Answer: All elements have a ΔHf of 0 (zero) at standard temperature and pressure.
Standard ΔHf of formation is the standard enthalpy (heat) of formation of the compound. It is defined as the change of enthalpy when one mol of compound is formed in its standard state from the elements in their standard state.
Then, as the elements are already in their standard state, there is not any change and the standard enthalpy of an element in its standard state is, by definition, zero.
