Which of the following elements from Period 3 of Periodic table, has the largest ionic radius when forms a stable ion?
Correct answer: C. Phosphorous
- A. Sodium
- B. Silicon
- C. Phosphorous
- D. Chlorine
Explanation
In period 3, phosphorus forms the P3 minus ion, which has three extra electrons on a nucleus of 15 protons and so is the largest ion. Cl minus has more protons holding the same 18 electrons, so it is smaller, and Na plus and Si4 plus lose their whole outer shell and are much smaller.
This question appeared on the UHS MDCAT 2026 paper, which you can sit online with every answer explained.
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About Periodic Properties and Trends
Periodic properties arise from electron configuration and effective nuclear charge, producing trends in atomic and ionic radius, ionization energy, electron affinity, electronegativity, metallic character and reactivity. Comparisons run across periods and down groups, with attention to common exceptions. The topic also relates these trends to the behavior of s-block and p-block elements.
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