Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out in the presence of

The formation of molecular complex $BF_3 – NH_3$ results in a change in hybridization of boron

The electronegativity of aluminium is similar to

In the following sets of reactants which two sets best exhibit the amphoteric characters of $Al_2O_3. xH_2O$ ?

Set $1$: $Al_2O_3 .xH_2O\, (s)$ and $OH^-(aq)$

Set $2$: $Al_2O_3 .xH_2O\, (s)$ and $H_2O\,(l)$

Set $3$: $Al_2O_3 .xH_2O\, (s)$ and $H^+(aq)$

Set $4$: $Al_2O_3 .xH_2O\, (s)$ and $NH_3(aq)$

The number of $2-$ centre $-2-$ electron and $3-$ centre $-2-$ electron bonds in $B_2H_6$, respectively, are