1. Moles = conc. * volume.
You need to convert the volume so its relative to the concentration first. 50 / 1000 = 0.05dm3. 0.10 mol dm-3 * 0.05dm3 = 0.005moles of sodium hydroxide.
However in aqueous solution NaOH will dissociate to form Na+ and OH- - two seperate species, of which you have 0.005moles of each.
So the answer is 0.005 + 0.005.
Remember if you started with ONE molecule of NaOH, this will become TWO ions. So the number of moles will double.