Which of the following statements is correct regarding boron hydrides?

In moist air,$AlCl_3$ fumes because:

Which of the following oxides is amphoteric in nature?

The tendency of $BF_3$,$BCl_3$ and $BBr_3$ to behave as Lewis acid decreases in the sequence

Addition of mineral acid to an aqueous solution of Borax,the following compound is formed:

In the following sets of reactants,which two sets best exhibit the amphoteric character of $Al_2O_3 \cdot xH_2O$?
Set $1$: $Al_2O_3 \cdot xH_2O_{(s)}$ and $OH^{-}_{(aq)}$
Set $2$: $Al_2O_3 \cdot xH_2O_{(s)}$ and $H_2O_{(l)}$
Set $3$: $Al_2O_3 \cdot xH_2O_{(s)}$ and $H^{+}_{(aq)}$
Set $4$: $Al_2O_3 \cdot xH_2O_{(s)}$ and $NH_{3(aq)}$