The atomic radius of elements decreases across a period because: MCQ with Answer and Explanation

The atomic radius of elements decreases across a period because:
A. Atomic mass decreases
B. Electron-electron repulsion decreases
C. Number of shells increases
D. Nuclear charge increases and electrons are added to the same shell
Answer: Option D
Solution (By JKExamLibrary)
Across a period, the number of electron shells remains the same, but the nuclear charge (protons) increases. The added electrons enter the same valence shell, so the effective nuclear attraction on the electrons increases, pulling them closer and shrinking the atomic radius. Down a group, radius increases due to addition of shells. Electron-electron repulsion alone does not account for the trend. Atomic mass generally increases across a period.

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Correct Answer: Option C


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