Question

In which among the following compounds , hydrogen shows a negative valency?

• A. H₂SO₄
• B. HCl
• C. NaHCO₃
• D. NaH

Answer 1

The correct option is D

NaH

• The atomic number of Hydrogen is one.
• The combining capacity of an element is called valency.
• The valency of hydrogen is one.
• Hydrogen attain +1 or -1 oxidation state depends upon the compound.
• It has only one electron to lose for +1 oxidation state and -1 oxidation state.
• The hydrogen anion (H^-) is formed when it captured an extra electron.

Explanation for correct answer

• (d) Sodium hydride (NaH)
• The electronic configuration of sodium is 2,8,1.
• When sodium combines with hydrogen , the one electron in the valence shell is transferred to hydrogen atom.
• So sodium becomes Na⁺ ion (cation) and hydrogen changes to H^- (anion).
• Sodium hydride (NaH) is an ionic compound.

Explanation for incorrect answer

• (a) H₂SO₄ sulphuric acid
• The valency of sulphate ion (SO₄^-2 ) is 2 it has an oxidation state ^- 2. Sulphate ion is a divalent negative ion.
• It combines with two hydrogen atoms. So hydrogen has +1 positive oxidation state..(cation)
• (b) HCl hydrochloric acd
• Chlorine has 7 valence electrons and its electron configuration is 2,8,7.
• One electron from hydrogen is moved towards chlorine and changed into H⁺ (cation) and chlorine changes to ,chloride ion Cl^-1. (anion).
• ( c ) NaHCO₃ sodium bicarbonate
• Bicarbonate (HCO₃^-1) is a monovalent polyatomic ion with valency 1.
• It is formed by the deprotonation of H₂CO₃.

Therefore hydrogen shows a negative valency in NaH.