What is the conjugate base of $[Al(H_2O)_3(OH)_3]$?

Conjugate acid of $NH_2^{-}$ and $NH_3$ are respectively

Among $CO_3^{2-}$,$OH^{-}$,$NH_3$ and $HCO_3^{-}$,the species that acts as a Bronsted acid as well as a Bronsted base,is

In the reaction where $HNO_3$ acts as a base,which of the following acts as the strongest acid?

Explain the statement: "$NH_3$ acts as both a Lewis base and a Brønsted-Lowry base,whereas $BF_3$ acts only as a Lewis acid but not as a Brønsted-Lowry acid."

Urea is preferred to ammonium sulphate as a nitrogenous fertilizer because