Ncert Exercises & Solutions

In which of the following pairs, the ions are isoelectronic?

1. Na⁺, Mg²⁺

2. Al³⁺, O^-

3. Na⁺, O^2-

4. N^3-, Cl^-

(a, c)

For,

{Na}^{+} = 11 - 1 = 10 e^{-}

{Mg}^{2 +} = 12 - 2 = 10 e^{-}

Thus, they have same number of electrons.

Fo,

{Al}^{3 +} = 13 - 3 = 10 e^{-}, O^{-} = 8 + 1 = 9 e^{-}

They do not have same number of electrons.

For,

{Na}^{+} = 10 e^{-}, O^{2 -} = 8 + 2 = 10 e^{-}

They have same number of electrons.

For,

N^{3 -} = 7 + 3 = 10 e^{-}, {Cl}^{-} = 17 + 1 = 18 e^{-}

They do not have same number of electrons.

Thus, Na⁺ is isoelectronic with Mg²⁺ and O^2-.