p Block Elements Part 3

Concept:Group 13 elements show periodic trends in ionic radii, electronegativity, ionisation enthalpy, and the nature of their halides.Explanation:Statement A: Ionic radii of trivalent cations ($\mathrm{B}^{3+}$, $\mathrm{Al}^{3+}$, $\mathrm{Ga}^{3+}$, $\mathrm{In}^{3+}$, $\mathrm{Tl}^{3+}$) increase down the group.So the radii do not decrease. Hence statement A is false.Statement B: The electronegativity order is $\mathrm{B} > \mathrm{Tl} > \mathrm{In} > \mathrm{Ga} > \mathrm{Al}$.This order shows irregular variation, not a simple decrease down the group. Hence statement B is false.Statement C: First ionisation enthalpy order is $\mathrm{B} > \mathrm{Tl} > \mathrm{Ga} > \mathrm{Al} > \mathrm{In}$.Boron has the highest first ionisation enthalpy among group 13 elements. Hence statement C is true.Statement D: Trichlorides ($\mathrm{MCl}_3$) and triiodides ($\mathrm{MI}_3$) of group 13 elements are covalent.The $\mathrm{M}^{3+}$ ion is small and highly charged, giving high polarising power that favours covalent bonding with halide ions. Hence statement D is true.Answer:Correct statements are C and D only. Option B is correct.