Question

When calcium metal is add to water the gas evolved does not catch fire but same gas evolved on adding sodium metal to water catch es fire

Answer 1

Ca + H2O ---------> CaO +H2(G)

This is the equation of the question asked as same gas is evolved in that case also H2 is only produced but there  Na is a highly reactive metaL and is inflamable when added to water

Answer 2

when calcium reacts with water hydrogen gas is evolved out but same gas evolved on adding sodium metal catches fire because sodium metal reacts with water and catches fire because it replaces hydragen from water and forms the compound sodium hydroxide