The cell potential for the given cell at $298 \mathrm{K} \mathrm{Pt}\left|{\mathrm{H}}_2\left(\mathrm{g},1 \mathrm{bar}\right)\right|\left|{\mathrm{H}}^{+}\left(\mathrm{aq}\right)\Vert {\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)\right|\mathrm{Cu}\left(\mathrm{s}\right)$ is $0.31 \mathrm{V}$. The $\mathrm{pH}$ of the acidic solution is found to be $3$, whereas the concentration of ${\mathrm{Cu}}^{2+}$ is ${10}^{\mathrm{x}} \mathrm{M}$. The value of $\mathrm{x}$ is _________.

(Given: ${\mathrm{E}}_{{\mathrm{Cu}}^{2+}/\mathrm{Cu}}^{\Theta }=0.34 \mathrm{V}$ and $\frac{2.303\mathrm{RT}}{\mathrm{F}}=0.06 \mathrm{V}$)

Hence, the correct answer is 7.