$Al$ having double conductivity as compared to which metal ?

In which of the following reaction, the hybridisation of the central atom changes from $sp^2$ to $sp^3$ ?

Anhydrous $AlC{l_3}$ is obtained from

Is boric acid a protic acid ? Explain. 

Consider the following statements for diborane 

$1.$  Boron is approximately $sp^3$ hybridized

$2.$  $B-H-B$ angle is $180^o$

$3.$  There are two terminal $B-H$ bonds for each boron atom

$4.$  There are only $12$ bonding electrons available

Of these statements

Purification of aluminium done by electrolytic refining is known as