Which of the following statements is true about ionic radius? Ionic radius

Analyze the question: It asks how ionic radius relates to nuclear charge (the number of protons in the nucleus).

Concept: Ionic radius is the size of an ion. Its size depends on how strongly the nucleus pulls on the electrons. The greater the nuclear charge, the stronger the attraction on the electron cloud, so the electrons are pulled closer and the radius gets smaller. This applies when we compare ions with the same number of electrons (isoelectronic ions) or move across a period.

Example (isoelectronic ions, each with 10 electrons):

| Ion | Protons (nuclear charge) | Electrons | Relative radius | |---|---|---|---| | O²⁻ | 8 | 10 | largest | | F⁻ | 9 | 10 | smaller | | Na⁺ | 11 | 10 | smaller still | | Mg²⁺ | 12 | 10 | smallest |

The electron arrangement is the same, but as the number of protons increases from 8 to 12, the electrons are drawn in more tightly and the radius decreases.

Checking the options:

• A. Incorrect. A larger nuclear charge does not enlarge the ion.
• B. Correct. The radius decreases as the nuclear charge increases.
• C. This is the reverse of the trend, so it is not the best statement. (It is technically the converse, since a lower charge gives a larger radius, but B is the standard statement.)
• D. Incorrect. The radius changes with nuclear charge.

Answer: B. Ionic radius decreases as nuclear charge increases.

Tip: Remember "more protons, stronger pull, smaller size" for isoelectronic ions. For a question on ions with the same electron count, rank them by proton number: the highest proton number gives the smallest radius.