\textbf{206.} The sum of the stoichiometric coefficients of the substances in the reaction:
$$\text{Na}_2\text{O}_2\text{(s)} + \text{H}_2\text{O(l)} \rightarrow \text{NaOH(aq)} + \text{O}_2\text{(g)}$$
after balancing, is:
(1) 8 \hfill (2) 9 \hfill (3) 10 \hfill (4) 11
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