The following results were obtained during study of the reaction \(2 \mathrm{NO}(\mathrm{g})+\mathrm{Cl}_2(\mathrm{~g}) \rightarrow 2 \mathrm{NOCl}(\mathrm{g})\). Determine the value of \([\mathrm{X}]\) in \(\mathrm{mol} / \mathrm{L}\)
\(\begin{array}{|c|c|c|c|} \hline \text{Experiment} & \text{[NO] mol/L} & \left[\mathrm{Cl}_2\right] \text{ mol/L} & \text{Initial rate of formation. [NOCl] mol/L/min} \\ \hline \text{I} & 0.2 & 0.2 & 6.0 \times 10^{-3} \\ \hline \text{II} & 0.2 & 0.4 & 2.4 \times 10^{-2} \\ \hline \text{III} & 0.4 & 0.2 & 1.2 \times 10^{-2} \\ \hline \text{IV} & X & 0.6 & 1.35 \times 10^{-1} \\ \hline \end{array}\)

1. A \([X]=0.4\)
2. B \([\mathrm{X}]=0.8\)
3. C \([\mathrm{X}]=0.3\)
4. D \([\mathrm{X}]=0.5\)