A positive charged ion denotes the loss of an electron & A negative charged ion represents the gain of an electron by a species.

For H⁺₂:

Number of electrons present in Hydrogen molecule = 2

So, Number of electrons present in H⁺₂ = 2 – 1

= 1

For H₂:

Number of electrons present in Hydrogen molecule = 2

For O⁺₂:

Number of electrons present in Oxygen molecule = 8 + 8

= 16

So, Number of electrons present in O⁺₂ = 16 - 1

= 15