A student heats 50g of reactant ‘A’ with 25g of reactant ‘B’. He obtains 25g of product ‘C’ and recovers 50g of unreacted ‘B’. Which of the following law is confirmed in the following reaction?

The law of conservation of mass states that matter cannot be created or destroyed. The law of definite proportions states that a given chemical compound always contains the same elements in the exact same proportions by mass.

As in question the student took a total of 75 gm of reactant therefore the amount of product obtained is also 75 gm and in same proportion of 25 and 50 gm as taken in reactants.