Question

Electropositive character for the elements of group 13 follows the order.

• A. B > Al > Ga > In > Tl
• B. B < Al < Ga < In <Tl
• C. B < Al > Ga < In > Tl
• D. B < Al > Ga > In > Tl

Answer 1

Answer: (D)

B < Al > Ga > In > Tl

Answer 2

: As we move from B to Al, the sum of $\Delta_{i}H_{1} + \Delta_{i}H_{2} + \Delta_{i}H_{3}$ decreases substantially (6887 KJ $mol^{- 1}$ to 5137 kJ $mol^{- 1}$) due to increase in the atomic size and hence Al has a high tendency to lose electrons. Since the electronde potentials increase from Al to Tl, therefore, their electronpositive character decreases, i.e., Al (- $1.66V$) to Ga $( - 0.56V)$ to In $( - 0.34V)$ to Tl $( + 1.26V)$ accordingly.