Here's a breakdown:

* Active Metals: These are metals that readily lose electrons and form positive ions (cations). Examples include:

* Group 1 (alkali metals): Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs)

* Group 2 (alkaline earth metals): Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba)

* Hydrogen: Hydrogen, in its elemental form (H₂), is a diatomic molecule.

* Reaction: Active metals react with hydrogen to form metal hydrides. In this process, hydrogen acts as an oxidizing agent, gaining electrons to form the hydride ion (H⁻). The metal loses electrons to form a positive ion (e.g., Na⁺).

Example:

Sodium (Na) reacts with hydrogen gas (H₂) to form sodium hydride (NaH):

2Na(s) + H₂(g) → 2NaH(s)

Important Notes:

* Metal hydrides are ionic compounds where the metal cation is bonded to the hydride anion.

* These reactions typically require high temperatures and pressures.

* Metal hydrides are often used as reducing agents and in the synthesis of other compounds.