Question

When Ca metal is added to water, the gas evolved doesn't catch fire but the same gas evolve on adding Na metal to water catches fire. Why is it so?

Answer 1

Sodium is a highly reactive alkali metal. That means it has a single electron in its outer shell which is readily lost in reactions, resulting in a much more stable, complete outer electron shell. When sodium comes in contact with water, hydrogen gas is liberated with an explosion.

Ca is not that much reactive. So in this case, gas does not catches fire