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Q11 (CISF/2026) Science & Technology › Basic Science (Physics, Chemistry, Biology)

Consider the following : 1. Ionic radius order : Na+ < Mg2+ < Al3+ < Si4+ 2. Atomic radius order : Si < Al < Mg < Na 3. Effective nuclear charge : Na < Si < Mg < Al Which of the above is/are correct ?

Result
Your answer: —  Â·  Correct: D

Explanation

The statements evaluate periodic trends for elements in Period 3 (Na, Mg, Al, Si):

  • Statement 1 is incorrect: Na+, Mg2+, Al3+, and Si4+ are isoelectronic species (all have 10 electrons). As the nuclear charge (atomic number) increases from Na (11) to Si (14), the nucleus exerts a stronger pull on the electrons, causing the ionic radius to decrease. The correct order is Na+ > Mg2+ > Al3+ > Si4+.
  • Statement 2 is correct: Across a period from left to right, the atomic radius decreases because the effective nuclear charge increases while the number of electron shells remains the same. Thus, Na > Mg > Al > Si.
  • Statement 3 is incorrect: Effective nuclear charge (Zeff) increases steadily across a period as more protons are added to the nucleus. The correct order is Na < Mg < Al < Si.

Therefore, only statement 2 is correct.

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