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 $\Delta_iH_1 + \Delta_iH_2 + \Delta_iH_3$ 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 electrode potentials increase from $Al$ to $Tl$, therefore, their electropositive character decreases, i.e., $Al (- 1.66\, V)$ to $Ga (- 0.56 \,V)$ to $In (- 0.34\, V)$ to $Tl (+ 1.26\, V)$ accordingly.