Which of the following is acidic in nature ?

Options

A. `Be(OH)_(2)`
B. `Mg(OH)_(2)`
C. `B(OH)_(3)`
D. `Al(OH)_(3)`

Answer

C

Explanation

`B(OH)_(3)` in aqueous medium coordinates a molecule of water to form the hydrated species .In this species,`B^(3+)` ion,because of its small size,exercises a high polarizing power thereby pulling the sigma electeron charge of the coordinated O atom towards itself.The coordinated oxygen,in turn,pulls the sigma electron charge of the OH bond of the attached `H_(2)O` molecule towards itself.This facilitates the removal of `H^(+)` ion from the O-H bonds,as shown below
Thus the solution of `B(OH)_(3)` in water as a weak acid.That is why it reacts with `NaOH` solution to produce the sodium salt.
`B(OH)_(3)+NaOH hArr Na^(+)[B(OH)_(4)]^(-)`
`hArr Na^(+)BO_(2)^(-)+2h_(2)O`
sodium metaborate.