Why is octasulfur present in equation for standard enthalpy of formation of sulfuric acid?


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> Write a balanced chemical equation corresponding to the standard enthalpy of formation of $\ce{H2SO4}.$
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\eqref{rxn:r1} is the given answer, \eqref{rxn:r2} is my answer:


\begin{align}
\ce{1/8 S8 (s) + H2(g) + 2 O2(g) &-> H2SO4(l)} \label{rxn:r1}\tag{R1}\\
\ce{S(s) + H2(g) + 2 O2(g) &-> H2SO4(l)} \label{rxn:r2}\tag{R2}
\end{align}


How can I know I have to use $\ce{S8}$ rather than simply $\ce{S}$?




Here is a definition of [standard enthalpy of formation](https://en.m.wikipedia.org/wiki/Standard_enthalpy_of_formation) from Wikipedia.



> 
> The standard enthalpy of a compound is the change of enthalpy in formation of one mole of the substance from its constituent elements, with all substances in their standard states.
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So according to it, the constituent elements should be in their standard states. Now coming to question, the standard state of sulphur is *rhombic sulphur* and it exists as $\ce{S8}$ molecule in nature but not simply as individual atoms.


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