Question

Arrange the given elements in the increasing order of their atomic radius.
$\text{sodium, potassium, magnesium, rubidium}$

A) $\text{magnesium < potassium < sodium < rubidium}$
B) $\text{magnesium < sodium < potassium < rubidium}$
C) $\text{magnesium < sodium < rubidium < potassium}$
D) $\text{sodium < potassium < rubidium< magnesium}$

[1 Mark]

Answer 1

Correct answer: B) $\text{magnesium < sodium < potassium < rubidium}$
[1 Mark]

The atomic radius decreases across a period (from left to right).
$\text{Mg}$ lies on the right side of $\text{Na}$ and hence, atomic radius of magnesium is less than that of sodium.
Also, the atomic radius increases down a group due to the addition of new shells (energy levels).
$\text{K}$ lies below $\text{Na}$ in the same group and hence, the atomic radius of potassium is greater than that of sodium.
Similarly, $\text{Rb}$ is in the same group of $\text{K}$ and $\text{Na}$ and lies below them. Hence, rubidium has the largest size.
Thus the correct answer is: $\text{Mg < Na < K < Rb}$