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Periodic Table and Periodicity question

2025 · 29 Jan · Shift 1 · Q20
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Periodic Table and Periodicity question

2025 · 29 Jan · Shift 1 · Q20

JEE MainChemistryPeriodic Table and PeriodicityMCQ+4 / −1
Given below are two statements : Statement (I) : The radii of isoelectronic species increases in the order. Mg2+Mg^{2+}Mg2+ < Na+Na^+Na+ < F −-− < O2−O^{2-}O2− Statement (II) : The magnitude of electron gain enthalpy of halogen decreases in the order. Cl > F > Br > I In the light of the above statements, choose the most appropriate answer from the options given below :
  1. A
    Statement I is incorrect but Statement II is correct
  2. B
    Both Statement I and Statement II are correct
  3. C
    Statement I is correct but Statement II is incorrect
  4. D
    Both Statement I and Statement II are incorrect
View written solutionFree

Correct answer: B

  1. Analyze Statement (I): Isoelectronic species

    The species given are: Mg2+, Na+, F−, O2−Mg^{2+},\ Na^+,\ F^-,\ O^{2-}Mg2+, Na+, F−, O2−

    Let us count electrons in each:

    • Mg2+Mg^{2+}Mg2+: 12−2=1012-2=1012−2=10
    • Na+Na^+Na+: 11−1=1011-1=1011−1=10
    • F−F^-F−: 9+1=109+1=109+1=10
    • O2−O^{2-}O2−: 8+2=108+2=108+2=10

    So all are isoelectronic; each has 10 electrons.

    For isoelectronic species, radius decreases as nuclear charge ZZZ increases, because the same number of electrons is pulled more strongly by a larger positive charge.

    Nuclear charges are:

    • MgMgMg: Z=12Z=12Z=12
    • NaNaNa: Z=11Z=11Z=11
    • FFF: Z=9Z=9Z=9
    • OOO: Z=8Z=8Z=8

    Therefore, size order is: Mg2+<Na+<F−<O2−Mg^{2+} < Na^+ < F^- < O^{2-}Mg2+<Na+<F−<O2−

    This matches Statement (I). So Statement (I) is correct.

  2. Analyze Statement (II): Electronegativity order

    Among halogens, electronegativity decreases down the group: F>Cl>Br>IF > Cl > Br > IF>Cl>Br>I

    Hence the given order is correct. So Statement (II) is correct.

  3. Choose the correct option

    Since both statements are correct, the correct option is: B\boxed{B}B​

  4. Compare with stored answer

    Stored correct answer: B

    Our derived answer also: B

    Hence, they agree.

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