Which gas can be adsorbed on a metal and released when required?

Which of the following elements will form an acidic oxide?

Which catalyst is used to increase the rate of the vulcanization process of rubber?

An alloy has a low melting point and is,therefore,used for electrical fuses. Name the alloy and write its constituents.

An element $A$ is soft and can be cut with a knife. It is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following:

How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?