Analyzing statements about Group 13 elements (B, Al, Ga, In, Tl):
A. Ionic radii of M³⁺ cations: Down a group, more electron shells are added, so ionic radii increase, not decrease. FALSE
B. Electronegativity: Generally decreases down the group, though Ga shows an anomaly with higher electronegativity than Al. The statement is approximately true but has exceptions.
C. First ionization enthalpy: B (800.6 kJ/mol) is highest due to smallest size and highest nuclear charge density. Al (577.5), Ga (579), In (558), Tl (589). TRUE
D. Trichlorides and triodides: BCl₃, AlCl₃, GaCl₃, etc. are all covalent compounds (electron-deficient). BI₃, AlI₃, GaI₃, etc. are also covalent (I⁻ is large and polarizable). TRUE
The clearly correct statements are C and D.