Question

Arrange the following elements in order of decreasing atomic size.
Phosphorous, sulphur, carbon, nitrogen

Answer 1

Down a group: The increase in number of valence shells overcomes the increased nuclear charge. Hence, atomic size increases. [0.5 Mark]

Across a period: Number of valence shells remain the same which cannot overcome the increased nuclear charge. Hence, atomic size decreases from left to right in a period. [0.5 Mark]
$$\begin{array}{ccc}\text{14}& \text{15}& \text{16}\\ \text{C}& \text{N}& \\ & \text{P}& \text{S}\end{array}$$

So, the correct order of atomic size is as follows:
P > S > C > N

[1 Mark]