Ionic hydrides are commonly known as saline hydrides or pseudohalides. These compounds form between hydrogen and the most active metals, especially with the alkali and alkaline-earth metals of group one and two elements. In this group, the hydrogen acts as the hydride ion (H−).

NaH, or sodium hydride, is an inorganic compound that consists of sodium (Na) and hydrogen (H) atoms. When NaH is added to water (H2O), it undergoes a reaction that produces a large amount of energy. This energy release is due to the formation of an ionic hydride.

Ionic Hydride Formation:
- When NaH is added to water, the following reaction occurs: NaH + H2O -> NaOH + H2.
- In this reaction, the sodium hydride (NaH) reacts with water (H2O) to form sodium hydroxide (NaOH) and hydrogen gas (H2).
- The formation of sodium hydroxide and hydrogen gas is accompanied by the release of a large amount of energy.
- This energy is released because the reaction involves the transfer of electrons from sodium to water, resulting in the formation of sodium ions (Na+) and hydroxide ions (OH-).
- The transfer of electrons from sodium to water is an exothermic process, meaning it releases energy.

Explanation of the Correct Answer:
The correct answer to the question is option 'C' - ionic hydride. This is because NaH, when added to water, forms an ionic compound (sodium hydroxide) and releases a large amount of energy. Ionic compounds are formed by the transfer of electrons between atoms or ions, resulting in the formation of positive and negative ions. In the case of NaH, the transfer of an electron from sodium to water leads to the formation of Na+ ions and OH- ions, making it an ionic hydride.

Other Options:
- Option 'A' - interstitial hydride: Interstitial hydrides are formed when hydrogen atoms occupy the interstitial sites (voids) within the crystal lattice of a metal. NaH does not exhibit this behavior as it is not a metal.
- Option 'B' - covalent hydride: Covalent hydrides are formed when hydrogen atoms share electrons with another element, resulting in the formation of covalent bonds. NaH does not involve such covalent bonding as it undergoes an ionic reaction with water.
- Option 'D' - all of the above: This option is incorrect because NaH does not form interstitial or covalent hydrides when added to water. Only an ionic hydride is formed in this particular reaction.