Volume of water at STP which contains 10 moles of electrons is 

Water is a liquid having a density=1 g/ml.

 $\therefore$18 g = 18 ml;

Number of electrons in one molecule of ${\mathrm{H}}_2\mathrm{O}$ = 2(1) + 8 = 10

   18 ml of ${\mathrm{H}}_2\mathrm{O}$ contain $10{\mathrm{N}}_{\mathrm{A}}$ electrons (10 moles)