The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a 50% (mass by volume) solution of sodium hydroxide (NaOH). ‘A’ dissolved 50g of NaOH in 100 mL of water, ‘B’ dissolved 50g of NaOH in 100g of water while ‘C’ dissolved 50g of NaOH in water to make 100 mL of solution. Which one of them has made the desired solution and why?

Student ‘C’ has made the desired solution as 50% (mass by volume)
means 50 g of solute for every 100 mL of solution and not in 100 mL of solvent.

Mass by volume % = Mass of solute (in g)/Volume of solution (in mL) x 100

50/100 x 100 = 50% mass by volume

Student ‘A’ dissolved 50 g of NaOH in 100 mL of water (solvent).
Student ‘B’ dissolved 50 g of NaOH in 100 g of water (solvent).
Both A and B cannot make the desired solution.