Question

Which of the following ion is smallest in size?

• A.
• B. Na⁺
• C. O^2-
• D. F^-

Answer 1

The correct option is A

Let us look at the number of electrons and protons in each of the given ions:

$M{g}^{2+}$ $\Rightarrow$ Atomic Number=12; Protons=12; Electrons=10

$N{a}^{+}$ $\Rightarrow$ Atomic Number=11; Protons=11; Electrons=10

$O^{2-}$ $\Rightarrow$ Atomic Number=8; Protons=8; Electrons=10

$F^{-}$ $\Rightarrow$ Atomic Number=9; Protons=9; Electrons=10

Protons have positive charge and electrons have an equal but negative charge.

The more postive the charge, the smaller the ionic radius if number of electrons is same.

So $M{g}^{2+}$ is smallest in size.