Question

Which of the following is smallest in size?

• A. ${\mathrm{N}}^{3-}$
• B. ${\mathrm{O}}^{2-}$
• C. ${\mathrm{F}}^{-}$
• D. ${\mathrm{Na}}^{+}$

Answer 1

The correct option is D

${\mathrm{Na}}^{+}$

Explanation for correct option:

D. ${\mathrm{Na}}^{+}$

Cation:

• Cation is a positively charged species.
• When an atom loses its electrons, it leads to the formation of an ion, which is known as a cation.
• A cation is smaller in size because the nucleus holds the electrons more tightly, resulting in a smaller atomic size.

As a result, ${\mathrm{Na}}^{+}$ is the smallest in size out of all the given options.

Explanation for incorrect options:

• In the case of anions, there is an addition of electrons, the number of protons remains the same but the number of electrons gets changed.
• The repulsive forces become greater than the attractive forces of the positively charged nucleus due to which, the electron cloud of the anion expands and becomes bigger in size. Therefore, ${\mathrm{N}}^{3-}$, ${\mathrm{O}}^{2-}$ and ${\mathrm{F}}^{-}$ are larger in size than ${\mathrm{Na}}^{+}$.

As ${\mathrm{Na}}^{+}$ is the smallest in size. Thus options A, B, and C are incorrect.

Hence, the correct option is D i.e. ${\mathrm{Na}}^{+}$.