Question

The correct statements from the following are :
A. Ionic radii of trivalent cations of group 13 elements decreases down the group.
B. Electronegativity of group 13 elements decreases down the group.
C. Among the group 13 elements, Boron has highest first ionisation enthalpy.
D. The trichloride and triiodide of group 13 elements are covalent in nature.
Choose the correct answer from the options given below :

• A. C and D Only
• B. A and D Only
• C. A and C Only
• D. B and D Only

Hint:

Group 13 is full of anomalies! Always remember that Gallium is smaller than Aluminum in atomic radius due to the transition contraction, but the ionic radii follow a regular trend.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Group 13 (Boron family) elements exhibit unique trends due to the presence of d and f electrons in heavier elements, which causes poor shielding effects.
Step 2: Detailed Explanation:
Statement A is incorrect: Ionic radii of trivalent cations actually increase down the group (\(B^{3+}<Al^{3+}<Ga^{3+}<In^{3+}<Tl^{3+}\)).
Statement B is incorrect: Electronegativity first decreases from B to Al and then marginally increases down to Tl due to poor shielding by d and f electrons.
Statement C is correct: Boron is the smallest element in the group with the highest nuclear charge-to-radius ratio, giving it the highest first ionization enthalpy.
Statement D is correct: Most trihalides (except \(AlF_3\) and some thallium salts) are predominantly covalent due to the high charge density of the \(M^{3+}\) ion (Fajans' Rule).
Step 3: Final Answer:
The correct statements are C and D only.