Question

Which of the following statements about hydrogen is incorrect?
A. Hydrogen has three isotopes of which tritium is the most common
B. Hydrogen never acts as cation in ionic salts
C. Hydronium ion, \[{{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\] exists freely in solution
D. Dihydrogen does not act as a reducing agent

Answer 1

Hint: In the periodic table, hydrogen occupies the first position. It is the element having one electron in the valence shell. The molecule of hydrogen is present as a diatomic molecule, that is, \[{{\rm{H}}_{\rm{2}}}\]. It has three isotopes namely, deuterium, protium, and tritium.

Complete Step by Step Solution:
The percentages of all the isotopes of hydrogen namely protium, deuterium and tritium are 99.98%, 0.015% and \[{10^{ - 15}}\% \] . Therefore, the most abundant isotope is protium. So, Statement A is incorrect.

Statement B says, in ionic salts, hydrogen never behaves as a cation. For example, in the ionic salt of NaH, hydrogen acts as an anion. Therefore, the B option is true.

Statement C says the free existence of hydronium ions in solution. This statement is correct.

Statement D says that dihydrogen does not behave as a reducing agent. This statement is incorrect because the passing of hydrogen gas over metallic oxide of lead, copper, iron, etc removes the oxygen from the metal oxides and reduces them to the corresponding metal. Therefore, dihydrogen is a good reducing agent. Therefore, D is also incorrect.
Hence, A and D are correct options.

Note: Hydrogen is the most lightweight element and it possesses an atomic weight of 1.008 u. It is one of the important elements and because of its lightweight, it is found in abundance on Earth. On Earth, it exists in molecular forms such as water or other organic compounds.