Answer:
This is because of the release of hydrogen gas in the reaction.
Explanation:
Metals react with water and produce a metal oxide and hydrogen gas. It also starts floating due to the bubbles of hydrogen gas sticking to its surface.
For eg:
2Mg. + 2H2O --------> 2MgOH + H2
Here,
Metal taken is magnesium(2Mg) which when reacts with water(2H2O) to form its oxide form (2MgOH) and hydrogen gas(H2) is released which comes outside water as bubbles.
