Question

Which of the following species is isoelectronic with the hydride ion?

• A. $H^{+}$
• B. $H{e}^{+}$
• C. He
• D. Be

Answer 1

The correct option is C He

Isoelectronic species are those which have the same number of electrons.
Hydride ion $\left(H^{-}\right)$ contains 2 electrons. The $He$ atom also contains 2 electrons. Hence, they are isoelectronic.