JEE Main 2025 Apr 3 Shift 2, Chemistry Q18: Periodicity In Atomic Properties

JEE Main2025Apr 3, Shift 2Chemistry

The correct orders among the following are

A. Atomic radius : B $<$ Al $<$ Ga $<$ In $<$ Tl

B. Electronegativity : Al $<$ Ga $<$ In $<$ Tl $<$ B

C. Density : Tl $<$ In $<$ Ga $<$ Al $<$ B

D. 1st Ionisation Energy : In $<$ Al $<$ Ga $<$ Tl $<$ B

Choose the correct answer from the options given below :

A
B and D Only
B
A and C Only
C
C and D Only
D
A and B Only

Solution

Group 13 trends are irregular due to poor shielding from filled d and f subshells.

Atomic radii (pm): B 88, Al 143, Ga 135, In 167, Tl 170. The order is B $<$ Ga $<$ Al $<$ In $<$ Tl (Ga is smaller than Al due to d-block contraction), so statement A is wrong.

Electronegativity (Pauling): B 2.0, Al 1.5, Ga 1.6, In 1.7, Tl 1.8. The order Al $<$ Ga $<$ In $<$ Tl $<$ B is exactly correct, so B is right.

Densities (g cm $^{- 3}$ ): B 2.35, Al 2.70, Ga 5.91, In 7.31, Tl 11.85. Density increases down the group: B $<$ Al $<$ Ga $<$ In $<$ Tl, which is the reverse of statement C, so C is wrong.

First ionisation energies (kJ mol $^{- 1}$ ): B 801, Al 577, Ga 579, In 558, Tl 589. Order: In $<$ Al $<$ Ga $<$ Tl $<$ B, exactly matching statement D.

$∴$ Only B and D are correct.

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JEE Main 2025 Apr 3 Shift 2, Chemistry Q18: Periodicity In Atomic Properties

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