$18.4 \, A$ current is passed for $1$ hour and $42$ minutes through $CuSO_4$ solution using graphite electrodes at $298 \, K$ temperature and $1 \, bar$ pressure. If the cell efficiency is $75 \%$,calculate the mass of $Cu$ deposited and the volume of $O_2$ gas evolved at $STP$. $[Cu = 63.5 \, u, O = 16 \, u, R = 0.08314 \, L \, bar \, K^{-1} \, mol^{-1}]$

(N/A) $1$. Total time in seconds: $t = (1 \times 3600) + (42 \times 60) = 6120 \, s$.
$2$. Total charge passed: $Q = I \times t = 18.4 \, A \times 6120 \, s = 112608 \, C$.
$3$. Effective charge due to $75 \%$ efficiency: $Q_{eff} = 112608 \times 0.75 = 84456 \, C$.
$4$. Moles of electrons: $n_{e^-} = \frac{84456}{96500} \approx 0.8752 \, mol$.
$5$. For $Cu$ deposition $(Cu^{2+} + 2e^- \rightarrow Cu)$: Moles of $Cu = \frac{0.8752}{2} = 0.4376 \, mol$.
Mass of $Cu = 0.4376 \times 63.5 = 27.79 \, g$.
$6$. For $O_2$ evolution $(2H_2O \rightarrow O_2 + 4H^+ + 4e^-)$: Moles of $O_2 = \frac{0.8752}{4} = 0.2188 \, mol$.
Volume of $O_2$ at $298 \, K$ and $1 \, bar$ using $PV = nRT$: $V = \frac{0.2188 \times 0.08314 \times 298}{1} = 5.42 \, L$.