NEET 2023 Physics and Chemistry Solved Paper Code F1

As we move down the group, due to poor shielding effect of intervening d and f orbitals, the increased effective nuclear charge holds ns electrons tightly and therefore restricting their participation in bonding.
So, the relative stability of +1 O.S increases for heavier elements.
E∘ for ln3+∣In+=−0.16V
E∘ for Tℓ3+∣Tℓ+=+1.6V
Hence, TℓI is more stable than Tℓl3