Benzene exists as a resonance hybrid and its bonds exhibit characteristics that are halfway between single and double bonds. Resonance hybrids are best defined as

Explanation:

We can only talk about resonance hybrid for a compound in which more than one structure is possible based on its observed chemical properties.

There are compounds whose chemical properties can not be satisfactorily explained on the basis of a single chemical structure. In the case of such compounds, we invoke the idea of resonance.

A resonance hybrid is a single structure drawn to represent a given chemical specie which exhibits resonance behaviour and can otherwise be represented on paper in the form of an average of two or more chemical structures separated each from the next by a double-headed arrow.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.