\((ii)\) \(Cr _{2} O _{3}\) is an amphoteric oxide.
\((iii)\) \(\operatorname{In} RuO _{4},\) \('Ru'\) is in \(+8\) oxidation state. So it act as oxidising agent.
\((iv)\) Red colour of ruby is due to the presence of \(Cr ^{+3}\) ions in \(Al _{2} O _{3}\)