The cell potential for the given cell at \( 298 \, \mathrm{K} \)
\( \mathrm{Pt \, | \, H_2(g,\,1 \, bar) \, | \, H^+(aq) \, || \, Cu^{2+}(aq) \, | \, Cu(s)} \)
is \( 0.31 \, \mathrm{V} \). The pH of the acidic solution is found to be \( 3 \), whereas the concentration of \( \mathrm{Cu^{2+}} \) is \( 10^{-x} \, \mathrm{M} \). The value of \( x \) is ______.
(Given : \( E^\ominus_{\mathrm{Cu^{2+}/Cu}} = 0.34 \, \mathrm{V} \) and \( 2.303RT/F = 0.06 \, \mathrm{V} \) )