\textbf{228.} In an experiment, $0.5$ mol $\mathrm{N_2(g)}$, $0.5$ mol $\mathrm{O_2(g)}$, and $0.25$ mol $\mathrm{NO(g)}$ are introduced into a $250\,\mathrm{mL}$ flask and allowed to reach equilibrium for the reaction:
$$\mathrm{N_2(g) + O_2(g) \rightleftharpoons 2NO(g)},\quad K = 4\times10^{-4}$$
The concentration of gas $\mathrm{NO}$ at equilibrium is approximately how many $\mathrm{mol\cdot L^{-1}}$?
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(1) $1/1$ \hfill (2) $1/05$ \hfill (3) $0/05$ \hfill (4) $0/1$
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