Which elements of group $13$ possess both $+1$ and $+3$ oxidation state?

Conc. $HNO_3$ can be stored in a container of

Which one of the following statements is correct?

$A$ nonmetallic element of group $13$,used in making bulletproof vests,is an extremely hard solid of black colour. It can exist in many allotropic forms and has an unusually high melting point. Its trifluoride acts as a Lewis acid towards ammonia. The element exhibits a maximum covalence of four. Identify the element and write the reaction of its trifluoride with ammonia. Explain why the trifluoride acts as a Lewis acid.

Which hydrated elements of group $13$ are found as polymers in nature?

The set of amphoteric oxides among the given oxides are $Ga_2O_3, As_4O_{10}, Sb_4O_{10}, B_2O_3, Tl_2O$.