Which one of the following is known as lunar caustic when in fused state?

$MnO^{-}_4$ is of intense pink colour,though $Mn$ is in $(+7)$ oxidation state,it is due to

Corundum is

Which of the following is amphoteric?

$Fe_2Cr_2O_4 + Na_2CO_3 + O_2$ $\xrightarrow{\text{Fusion}} [X]$ $\xrightarrow[H_2O]{H^{+}} [Y]$ $\xrightarrow{H_2O_2/H^{+}} [Z]$
Which of the following statements is true for the compounds $[X]$,$[Y]$,and $[Z]$?

Which of the following is the correct formula for a compound of scandium and oxygen?