How many grams of NaOH are needed to make 250 mL of a 0.1 M solution?

Molarity tells you moles of solute per litre of solution. First find moles needed: moles = molarity times volume in litres = 0.1 times 0.250 = 0.025 mole. Next convert moles to grams using the molar mass of NaOH. Na is 23, O is 16, H is 1, so molar mass = 23 + 16 + 1 = 40 g/mol. Now mass = moles times molar mass = 0.025 times 40 = 1.0 g. So you dissolve 1.0 g of NaOH and make the solution up to 250 mL. The key is always converting millilitres to litres first (250 mL = 0.250 L), then using moles as the bridge between molarity and mass. This same three-step chain works for any molarity calculation in JEE.