JEE Chemistry 2026 Question with Solution

Given: Four statements about group $13$ elements are to be checked.

Find: Which statements are correct and hence the correct option.

Step 1: Understanding the concept Group $13$ elements show irregular trends because heavier members are affected by poor shielding of $d$ and $f$ electrons.

Step 2: Check each statement

Statement A is incorrect. The ionic radii of trivalent cations increase down the group:

So they do not decrease down the group.

Statement B is incorrect. Electronegativity does not decrease uniformly down the group. It decreases from B to Al and then shows a marginal increase towards Tl because of poor shielding by $d$ and $f$ electrons.

Statement C is correct. Boron has the highest first ionisation enthalpy in the group because of its small size and high effective nuclear attraction.

Statement D is correct. The trichlorides and triiodides of group $13$ elements are generally covalent in nature due to high charge density of the $M^{3+}$ ion, in accordance with Fajans' rule. The solution also notes exceptions such as $AlF_3$ and some thallium salts.

Conclude: Therefore, the correct statements are C and D only. Hence, the correct option is A.

Given: Statements A to D about trends and bonding in group $13$.

Find: Identify the true statements.

The key points are:

1. Ionic radii of $M^{3+}$ ions increase down the group.
2. Electronegativity is not a simple monotonic decrease in this group.
3. Boron has the highest first ionisation enthalpy.
4. Group $13$ trichlorides and triiodides are mainly covalent.

Thus:

• A is false.
• B is false.
• C is true.
• D is true.

Conclude: The correct combination is C and D only, so the answer is A.