d $(i)$ In $VOSO _{4},{ }^{\prime} V ^{\prime}$ is in $+4$ oxidation state. So it act as oxidising agent.
$(ii)$ $Cr _{2} O _{3}$ 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 $Al _{2} O _{3}$
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