# The pair of amphoteric hydroxides is :

$\begin{array}{1 1}(a)\;Be(OH)_2,Zn(OH)_2\\(b)\;Al(OH)_3,LiOH\\(c)\;B(OH)_3,B(OH)_2\\(d)\;Be(OH)_2,Mg(OH)_2\end{array}$

Down IIA,solubility of sulphates decreases and $BaSO_4$ is heavier than $CaSO_4$
Hence (b) is the correct answer.