The pair, in which ions are isoelectronic with $\mathrm{Al}^{3+}$ is :-

(D) $\mathrm{O}^{2-}$ and $\mathrm{Mg}^{2+}$

(A) $\mathrm{Br}^{-}$ and $\mathrm{Be}^{2+}$

(B) $\mathrm{Cl}^{-}$ and $\mathrm{Li}^{+}$

(C) $\mathrm{S}^{2-}$ and $\mathrm{K}^{+}$

JEE Main · 2022 · 25 Jun 2022 · Shift 1 · Atomic Structure

The pair, in which ions are isoelectronic with

Al^{3 +}

is :-

Answer: (D)

Isoelectronic species have the same number of electrons.

Al^{3 +}

has 13 - 3 = 10 electrons.

Checking each option:
(A)

Br^{-}

has 36 electrons,

Be^{2 +}

has 2 electrons
(B)

Cl^{-}

has 18 electrons,

Li^{+}

has 2 electrons
(C)

S^{2 -}

has 18 electrons,

K^{+}

has 18 electrons
(D)

O^{2 -}

has 8 + 2 = 10 electrons,

Mg^{2 +}

has 12 - 2 = 10 electrons

Therefore,

O^{2 -}

and

Mg^{2 +}

are both isoelectronic with

Al^{3 +}

, all having 10 electrons.

JEE Main · 2022 · 25 Jun 2022 · Shift 1 · Single correct option