Question

Answer in one word.
Which gas is evolved at cathode during the electrolysis of an aqueous solution of $NaCl$?

Answer 1

Reduction occurs at cathode. Water is reduced (in preference to sodium cations) to form hydrogen gas.
$2H_{2}O\left(l\right)+2e^{-}\to H_2\left(g\right)+2O{H}^{-}\left(aq\right)$
The standard reduction potential for reduction of water is higher than that for the reduction of $N{a}^{+}$ ions.
Hence, water has much greater tendency to get reduced than $N{a}^{+}$ ions.