What are the enthalpies of the elements and what are the standard states of enthalpies elements? * Unity * Zero * Negative * Positive

The enthalpy of formation depends upon the conditions of formation. i.e. temperature, pressure and physical state (gas solid or liquid) or allotropic state of the reactants. If all the reactants of a chemical reactions are in their standard state (i.e. at 25 degree C and 1 atmospheric pressure), the heat of formation or enthalpy of formation is called standard heat of formation or standard heat of formation.
By definition, the standard enthalpy (heat) of formation of an element in its standard state is zero, H_f^o = 0.