JEE Main · 2021 · 24 Feb 2021 · Shift 2 · d and f Block Elements

In $\mathrm{VOS}{\mathrm{O}}_4$ vanadium is in the $+4$ state, well below its maximum of $+5$, so it is readily oxidised and acts as a reducing agent. In $\mathrm{Ru}{\mathrm{O}}_4$ ruthenium is in its highest $+8$ state and can only gain electrons, so it is an oxidising agent. $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3$ dissolves in acids to give chromium(III) salts and in alkalis to give chromites, so it is amphoteric. Ruby is $\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$ in which a small fraction of the $\mathrm{A}{\mathrm{l}}^{3+}$ sites is taken by $\mathrm{C}{\mathrm{r}}^{3+}$, and the $d$-$d$ transitions of that $\mathrm{C}{\mathrm{r}}^{3+}$ give the red colour, so the statement ascribing the red colour of ruby to $\mathrm{C}{\mathrm{o}}^{3+}$ is the incorrect one.