Is Matter Around Us Pure

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?