Question

Which hydride among the following is less stable?

• A. HF
• B. BeH₂
• C. NH₃
• D. LiH

Answer 1

The Correct Option is B

The stability of hydrides is influenced by factors like bond strength and the nature of the bonds between hydrogen and the accompanying element. In this case, we're evaluating the stability of hydrides: HF, BeH₂, NH₃, and LiH. Let's analyze them for stability:

1. HF (Hydrofluoric Acid):

   HF is a covalent hydride with strong hydrogen bonds due to high electronegativity of fluorine. The strong H-F bond contributes to its stability. Hence, HF is quite stable.

2. BeH₂ (Beryllium Hydride):

   BeH₂ is predominantly covalent but forms polymeric chains through bridging hydrogen atoms. Its small size and the nature of its bonding lead to lower stability compared to other covalent hydrides. Thus, BeH₂ is less stable.

3. NH₃ (Ammonia):

   NH₃ is a covalent hydride with strong N-H bonds due to nitrogen's high electronegativity and the lone pair that allows hydrogen bonding. This gives NH₃ stability.

4. LiH (Lithium Hydride):

   LiH is ionic in nature, formed by the transfer of an electron from lithium to hydrogen. The strong ionic bond provides this compound with significant stability.

From this analysis, it is clear that BeH₂ is the least stable hydride due to weak polymeric nature and the absence of strong bonds like hydrogen bonds or ionic character. Therefore, the correct answer is BeH₂.