In making gun-barrel,the steel used is

Which of the following are used as catalysts in petroleum cracking?

Which of the following is an amphoteric oxide?

$KMnO_4$ decomposes on heating at $513 \ K$ to form $O_2$ along with

$NaCl$ reacts with conc. $H_2SO_4$ and $K_2Cr_2O_7$ to give reddish fumes $(B)$,which react with $NaOH$ to give yellow solution $(C)$. $(B)$ and $(C)$ respectively are:

Which of the following compounds is amphoteric?