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