Question

Which of the following is not isoelectronic?
(a) $Na ^{+}$
(b) $Mg ^{2+}$
(c) $O ^{2-}$
(d) $Cl ^{-}$

• A. 1 and 2 are correct
• B. 2 and 3 are correct
• C. 1 and 4 and correct
• D. 1,2 and 4 are correct

Answer 1

Answer: (D)

Isoelectronic species have same' number of electrons. $Mg ^{2+}, O ^{2-}$ and $Na ^{+}$have $10$ electrons hence, these are isoelectronic while $Cl$ has $18$ electrons hence, it is not isoelectronic.