Question

a metal which sinks in the surface of cold water to form hydrogen gas​

Answer 1

Explanation:

calcium is a metal which sinks in the surface of cold water to form hydrogen gas...

so, answer is calcium....

hope it helps you!

Answer 2

Sodium- 11

When sodium metal reacts with water, the resulting heat melts the metal almost immediately into a grey-silver ball. The hydrogen gas evolved during this reaction propels the ball rapidly across the surface of the water, leaving a white trail of sodium hydroxide that eventually dissolves into a clear solution. The hydrogen will often self-ignite and burn with an orange flame. Larger pieces of sodium metal may explode in contact with water.

Calcium- 17

When mixed with water, calcium metal generates hydrogen gas and forms a cloudy white solution of calcium hydroxide.