How many grams of KCl would I need in order to make 250 mL of a 0.25 M KCl solution.?

Number of moles of KCl
= Molarity × (Volume of solution in L)
= (0.25 mol/L) × (250/1000 L)
= 0.0625 mol

Molar mass of KCl = (39.01 + 35.45) = 74.46 g/mol

Mass of KCl
= (Number of moles) × (Molar mass)
= (0.0625 mol) × (74.46 g/mol)
= 4.65 g