Question

Oxidation number of $Cr$ in $Cr{O}_5$ is:

• A. $+10$
• B. $+6$
• C. $+4$
• D. $+5$

Answer 1

The correct option is B $+6$

$Cr{O}_5$ has one $Cr=O$ double bond. The oxygen atom of this double bond has oxidation number of $-2$. The remaining 4 oxygen atoms are part of peroxide linkages. The oxygen atom of peroxide linkage has oxidation number of $-1$. Let, X be the oxidation number of $Cr$

$X+(-2)+4(-1)=0$
$X-2-4=0$
$X=+6$
Hence, the oxidation number of $Cr=+6$