Which of the following compounds is amphoteric?

$I$. $4FeCr_2O_4 + 16NaOH + 7O_2 \rightarrow 8Na_2CrO_4 + 2Fe_2O_3 + 8H_2O$ (where $A = Na_2CrO_4$)
$II$. $2Na_2CrO_4 + H_2SO_4 \rightarrow Na_2Cr_2O_7 + Na_2SO_4 + H_2O$ (where $B = H_2SO_4$)
Compounds $(A)$ and $(B)$ are :

The products $A$ and $B$ formed in the following reactions are:
$CrO_2Cl_2 + 4NaOH \rightarrow A + 2NaCl + 2H_2O$
$A + 2HCl + 2H_2O_2 \rightarrow B + 3H_2O$

$Fe(OH)_2$ is precipitated from $Fe(II)$ solutions as a white solid but turns dark green and then brown due to the formation of:

On heating pyrolusite with $KOH$ in the presence of air,we get:

The color of acidified $K_2Cr_2O_7$ is not changed by: