Question

Which of the following correctly explains the atomic radius of magnesium compared to phosphorus?

• A. Magnesium has a larger atomic radius due to a smaller effective nuclear charge.
• B. Phosphorus has a larger atomic radius due to a larger effective nuclear charge.
• C. Magnesium has a larger atomic radius due to more electron levels.
• D. Phosphorus has a larger atomic radius due to fewer electron levels.

Answer 1

The correct option is A Magnesium has a larger atomic radius due to a smaller effective nuclear charge.

The element $Mg$ and $P$ are in the same period (third period) Thus $P$ experiences more effective nuclear charge as the effective nuclear charge increases towards the right. Thus the size of $Mg$ is larger as it has low effective nuclear charge. Hence the correct answer is option A.