| (1) $H_2(\text{g}) + O_2(\text{g}) \rightarrow H_2O_2(\text{l})$ | (2) $SO_3(\text{g}) + H_2O(\text{l}) \rightarrow H_2SO_4(\text{l})$ |
| [6pt] (3) $2F_2(\text{g}) + O_2(\text{g}) \rightarrow 2OF_2(\text{g})$ | (4) $Mg(\text{g}) + \dfrac{1}{2}O_2(\text{g}) \rightarrow MgO(\text{s})$ |
\textbf{218-} For which reaction can $\Delta H$ be considered as the standard enthalpy of formation of the product?
\begin{tabular}{ll}
(1) $H_2(\text{g}) + O_2(\text{g}) \rightarrow H_2O_2(\text{l})$ & (2) $SO_3(\text{g}) + H_2O(\text{l}) \rightarrow H_2SO_4(\text{l})$ \\[6pt]
(3) $2F_2(\text{g}) + O_2(\text{g}) \rightarrow 2OF_2(\text{g})$ & (4) $Mg(\text{g}) + \dfrac{1}{2}O_2(\text{g}) \rightarrow MgO(\text{s})$
\end{tabular}
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