The correct statements from the following are :
(A) The decreasing order of atomic radii of group 13 elements is Tl>In>Ga>Al>B.
(B) Down the group 13 electronegativity decreases from top to bottom.
(C) Al dissolves in dil. HCl and liberates H₂ but conc. HNO₃ renders Al passive by forming a protective oxide layer on the surface.
(D) All elements of group 13 exhibits highly stable +1 oxidation state.
(E) Hybridisation of Al in [Al(H₂ O)₆]³⁺ ion is sp³ d².
Choose the correct answer from the options given below :

Solution

Chemistry ma’am · 2 steps

Group 13 breaks its own trend at gallium: Ga is smaller than Al, and that knocks out (A) and (B).

1. The gallium anomaly. Gallium comes right after the first transition series, so it carries ten 3d electrons. These shield the nucleus poorly, so the outer electrons feel a stronger pull than expected. Ga ends up slightly smaller than Al and holds electrons a little more tightly.

   Statement	What is actually true	Verdict
   (A) Radii order	B 85, Al 143, Ga 135, In 167, Tl 170 pm, so the order is Tl > In > Al > Ga > B	False: Ga is smaller than Al
   (B) Electronegativity	B 2.0, Al 1.5, Ga 1.6, In 1.7, Tl 1.8: it falls from B to Al, then rises	False: not a steady decrease
   (C) Al with acids	2Al + 6HCl → 2AlCl₃ + 3H₂, while conc. HNO₃ forms a thin Al₂O₃ layer that stops further attack	True
   (D) +1 state	Inert pair effect makes +1 stable only for heavy members, mainly Tl. B and Al show only +3	False
   (E) [Al(H₂O)₆]³⁺	Six water ligands use one 3s, three 3p and two 3d orbitals of Al, giving an octahedral ion	True: sp³d²

2. So. Only (C) and (E) are correct, which is option (b).

The idea to keep. In group 13, expect gallium to break the trend: its poorly shielding 3d electrons make Ga smaller than Al and push electronegativity back up. The +1 state is stable only near the bottom, mainly for Tl.

Answer from the NTA final answer key. Solution by PrepWiser.