Q. 22

Which of the following statements about hydrogen are correct?
A. Hydrogen has three isotopes of which protium is the most common.

B. Hydrogen never acts as cation in ionic salts.

C. Hydrogen ion, H+ , exists freely in solution.

D. Dihydrogen does not act as a reducing agent.

Answer :

Hydrogen has three isotopes – Protium (1H1), Deuterium (2H1), Tritium (3H1). The number of neutrons is the reason why these isotopes differ from each other in spite of having the same atomic number.

Ordinary hydrogen, protium has no neutrons and thus the predominant form is protium.


When a hydrogen atom loses an electron, it forms a cation H+. But it is not at all stable to exist freely. The reason why any atom or molecule is formed is because the ionic forms cannot remain stable.


When H+ ion is formed, the size of the ion is very small (near about 10-3 pm. The normal atomic and ionic sizes vary from 50 to 230pm. Due to which, it cannot exist freely and it has to be always associated with other atoms or molecules to get stability. So it never acts as cation in ionic salt.

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