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JEE Advanced2026ChemistryClassification of Elements and Periodicity in PropertiesActual

The correct statement(s) regarding the periodic properties of elements is(are)

Options

  1. ASecond ionization enthalpy of carbon atom is less than that of boron atom.
  2. BIncreasing order of ionic radii: Al ³⁺ < Mg ²⁺ < Na ^+
  3. CUnder identical conditions, in solid state, the density of potassium metal is more than density of sodium meta
  4. DThe H - H bond is weaker than F - F bond.

Correct answer

A. Second ionization enthalpy of carbon atom is less than that of boron atom.

Step-by-step solution

For (A): The electronic configuration of B ^+ is 1s^2 2s^2 and that of C ^+ is 1s^2 2s^2 2p^1 . Removing an electron from the fully filled, more penetrating 2s orbital of B ^+ requires more energy than removing a 2p electron from C ^+ . Thus, the second ionization enthalpy of carbon is less than that of boron. Statement (A) is correct. For (B): Al ³⁺ , Mg ²⁺ , and Na ^+ are isoelectronic species with 10 electrons each. The nuclear charge increases in the order Na ^+ (11) For (C): The density of potassium ( 0.86 g/c

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