Which one of the following oxides dissolves in both hydrochloric acid and sodium hydroxide?

Tincal is

$A$ and $B$ are formed when borax is dissolved in water. $C$ and $B$ are formed when borax is reacted with aqueous $HCl$ solution. What are $A$ and $C$ respectively?

Give the names of the group $13$ elements.

Select the correct statements for diborane $(B_2H_6)$:
$1.$ Boron is approximately $sp^3$ hybridized.
$2.$ The $H-B-H$ bridge angle is $180^o$.
$3.$ There are two terminal $B-H$ bonds for each boron atom.
$4.$ There are only $12$ bonding electrons available.

Which hydroxides of group $13$ are amphoteric in nature?