Question

Which of the following metals directly combine with hydrogen gas to give a hydride?
(A) Au
(B) Ni
(C) Ca
(D) Cu

Answer 1

Hint : A hydride is formally the hydrogen anion, H⁻, in chemistry. The word is used in a broad sense. At one end, all molecules containing covalently bound H atoms are referred to as hydrides: water is an oxygen hydride, ammonia is a nitrogen hydride, and so on.

Complete Step By Step Answer:
Any of a group of chemical compounds in which hydrogen is paired with another element is referred to as a hydride. On the basis of the form of chemical bond concerned, three specific forms of hydrides can be distinguished: saline (ionic), metallic, and covalent.
Ca is the most reactive metal from Au, Ni, Ca, and Cu. As a result, it readily binds with H₂ to form hydride, while the other metals do not.
The following is an example of a reaction:
Ca + H₂ 🡪 CaH₂
The chemical compound calcium hydride, with the formula CaH₂, is an alkaline earth hydride. This grey powder (white if pure, which is uncommon) reacts quickly with water, releasing hydrogen gas. CaH₂ is thus used as a desiccant or drying agent.
Uses of Calcium hydride:
-Metal oxide reduction
-Source of Hydrogen
-Drying agent

Note :
CaH₂ is a saline hydride, which means it has a salt-like composition. Saline hydrides are formed by alkali metals and alkaline earth metals heavier than beryllium. Sodium hydride, which crystallises in the NaCl motif, is a well-known example. These species are insoluble in any solvent that does not react with them. CaH₂ crystallises as PbCl₂ (cotunnite) in the PbCl₂ structure.