Identify the reaction that does not obey the law of conservation of mass from the provided options.
 

1. 2Mg(s)+O2(g)2MgO(s)

2. C3H8(g)+O2(g)CO2(g)+H2O(g)

3. P4(s)+5O2(g)P4O10(s)

4. CH4(g)+2O2(g)CO2(g)+2H2O(g)

Hint: Law of conservation of mass

In this equation,
C3H8(g)44 g+O2(g)32 gCO2(g)44 g+H2O(g)18 g
i.e., mass of reactantsmass of products.
Hence, law of conservation of mass is not followed.