Question

Which of the following statements about hydrogen are correct?

• A. Hydrogen ion, $H^{+}$, exists freely in solution.
• B. Hydrogen has three isotopes of which protium is the most common.
• C. Hydrogen never acts as cation in ionic salts.
• D. Dihydrogen does not act as a reducing agent.

Answer 1

Answer: (B), (C)

Hydrogen never acts as cation in ionic salts.

A.Hydrogen has three isotopes: protium, ${(}_1^{1}H)$; deuterium, ${(}_1^{2}H)$ or D and tritium,${(}_1^{3}H$) or T. Among these, protium is the most common (99.98% abundance).

B.Hydrogen acts as anion in ionic salts like $NaH,BeH2,MgH2$. It does not act as cation in ionic salts.

C.Hydrogen ions, $H^{+}$ are highly unstable due to extremely small size. So, it does not exist freely. It gets hydrated/solvated and exists as $H_3{O}^{+}$ in solution.

D.Dihydrogen acts as an oxidising agent as well as reducing agent. It is used in reduction of the metallic ores. $CuO\left(s\right)+H_2\left(g\right)\to Cu\left(s\right)+H_{2}O\left(l\right)$

Hence, options (A) and (B) are correct.