Presence of $Cr$ in steel makes it

Which of the following compounds is amphoteric?

Generally,metal ions and their salts are coloured due to the presence of unpaired electrons in the metal ions. Which of the following compounds is coloured?

Which of the following has conductivity and appearance like that of copper metal?

Correct statements from the following are:
$A$. Potassium dichromate is an oxidising agent and it oxidises $FeSO_4$ to $Fe_2(SO_4)_3$ in acidic medium.
$B$. Sodium dichromate can be used as primary standard in volumetric estimation.
$C$. $CrO_4^{2-}$ and $Cr_2O_7^{2-}$ are interconvertible in aqueous solution by varying the $pH$ of the solution.
$D$. $Cr-O-Cr$ bond angle in $Cr_2O_7^{2-}$ is $126^\circ$.
Choose the correct answer from the options given below:

Which mineral among the following contains Vanadium in it?