Question

When a metal react with water it gives up hydrogen gas its reaction is

Mg + H2O = Mg(OH)2

Answer 1

Mg+H2O = Mg(OH)2+H2

When magnesium react with water it release magnesium hydroxide and hydrogen gas.

Answer 2

Mg + 2H2O ⇒ Mg(OH)2 + H2O

Magnesium starts floating as bubbles of hydrogen get stuck to the surface of the metal.