Answer
$2.1\times10^{4}\,g$
Work Step by Step
Charge= current$\times$ time
$=25\times10^{3}\,A\times 3600\,s=9.0\times10^{7}\,C$
As 1 mol of electrons has a charge equal to
96500 C, mols of electrons in $9.0\times10^{7}\,C$=
$\frac{9.0\times10^{7}\,C}{96500\,C/mol}=932.6425\,mol$
When 1 mol of electrons are consumed, 1 mol of Na(s) is formed according to the equation $Na^{+}(aq)+e^{-}\rightarrow Na(s)$
$\implies$ mols of Na= 932.6425 mol
Mass of Na= $number\,of\,moles\times molar\,mass $
$=932.6425\,mol\times22.99\,g/mol$
$=2.1\times10^{4}\,g$
