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JEE Main 2025 Apr 8 Shift 2, Chemistry Q7: Periodicity In Atomic Properties

JEE Main2025Apr 8, Shift 2Chemistry
Q.

The atomic number of the element from the following with lowest 1 ionisation enthalpy is:

  1. A

    32

  2. B

    35

  3. C

    87

  4. D

    19

Solution

The given atomic numbers correspond to germanium (32), bromine (35), francium (87) and potassium (19).

Ionisation enthalpy generally decreases down a group as atomic radius increases and shielding grows stronger.

Francium, sitting at the bottom of Group 1 with configuration , has an exceptionally large atomic radius and a heavily shielded outermost electron, making it easier to remove than the electrons of Ge, Br or K.

Therefore francium (atomic number 87) has the lowest first ionisation enthalpy among the given elements, matching option (3).

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