Answer:

Law of conservation of mass is also applicable to gases

For example:

2Na + 2HCl-> 2NaCl  + H₂

In this equation 46 g (23 x2 ) of sodium reacts with 73 (2{ 1 + 35.5}) g of HCl to produce 117 g(2{23+35.5)} of NaCl and 2 g of hydrogen gas

Since ,mass of reactants is equal to mass of products hence law of conservation of mass holds true.