Number of neutrons in a heavy hydrogen atom is

The hydride ion $H^{-}$ is isoelectronic with which of the following?

The hydride gap corresponds to elements of

Explain the laboratory preparation of dihydrogen.

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Physical properties of isotopes of hydrogen are different.
Reason $R$: Mass difference between isotopes of hydrogen is very large.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following statements is most applicable to hydrogen?