The number of compounds which are having only acidic nature is ________.
$Be(OH{)}_2,Mg(OH{)}_2,Al(OH{)}_3$ and $B(OH{)}_3$

$Mg(OH{)}_2$ is a weak base and $Be(OH{)}_2$ and $Al(OH{)}_3$ are amphoteric in nature.

$B(OH{)}_3$ can accept one hydroxyl ion from water and proton is released. Thus, it acts as a Lewis acid.

Hence, only one compound is acidic in nature.