Why hydrogen comes in reactivity series of metals????

and

How reactivity of hydrogen can be found out????????

Hydrogen is included in the reactivity series of the metals as it resembles alkali metals in some of its properties such as:

• It looses electron to form positive ion.
• It combines with non-metals which are electron attracting species.
• During hydrolysis if any hydride hydrogen gas is liberated at cathode.
• It acts as a strong reducing agent.

The reactivity of hydrogen is taken as a reference to find the reactivity of other metals. Metals that are more reactive than hydrogen are placed above hydrogen and the metals that are less reactive than hydroen are placed below hydrogen.