How many grams are there in 0.250 moles of NaOH?

We are asked to find the mass of 0.250 mol of NaOH

molar mass of NaOH - 40 g/mol

in other words 1 mol of NaOH has a mass of 40 g

therefore 0.250 mol of NaOH has a mass of - 40 g/mol x 0.250 mol = 10.0 g

mass of 0.250 mol of NaOH is 10.0 g