JEE Advanced 2018 · Paper 1, Chemistry question 10

For the electrochemical cell,

$$\ce{Mg(s) | Mg^{2+}(aq, 1 M) || Cu^{2+}(aq, 1 M) | Cu(s)}$$

the standard emf of the cell is 2.70 V at 300 K. When the concentration of $\ce{Mg^{2+}}$ is changed to $x$ M, the cell potential changes to 2.67 V at 300 K. The value of $x$ is ______.

(given, $\dfrac FR = 11500\ \mathrm{K\,V^{-1}}$, where $F$ is the Faraday constant and $R$ is the gas constant, $\ln(10) = 2.30$)