The incorrect statement among the following is

(a)  In ${\mathrm{VOSO}}_4{\cdot }^{\text{'}}{\mathrm{V}}^{\mathrm{\prime }}$ is in $+4$ oxidation state. So it act oxidizing agent.

(b) ${\mathrm{Cr}}_2{\mathrm{O}}_3$ s an amphoteric oxide

(c) In ${\mathrm{RuO}}_4{,}^{\text{'}}R{u}^{\mathrm{\prime }}$ is in $+8$ oxidation state So it act as oxidizing agent.

(d) Red colour of ruby is due to the presence of ${\mathrm{Cr}}^{+3}$ions in ${\mathrm{Al}}_2{\mathrm{O}}_3$