In electrolysis of aqueous NaCl, what volume of Cl2 (g) is produced in the time that it takes to liberate 5.0 litre if H2 (g)? Assume that both gases are measured at STP.

The overall reaction during the electrolysis of aquoeus sodium chloride:
$2NaCl\left(aq\right) + 2H_{2}O\left(l\right) \to 2N{a}^{+}\left(aq\right)+ 2O{H}^{-} \left(aq\right)+ C{l}_2 \left(g\right) + H_2 \left(g\right)$

It can be seen that 1 volume of hydrogen to 1 volume of chlorine is collected in the electrolysis.

So, 5 L of chlorine gas will be produced.