Question

What will be the oxidation number of Chromium $\left(Cr\right)$ in $Cr{O}_5$?

• A. $+5$
• B. $+6$
• C. $+10$
• D. $+2$

Answer 1

The correct option is B $+6$

In the above structure we can see that, 4 oxygen atomshave a peroxide linkage i.e. $(O-O)$ linkage.
So oxidation state of those 4 oxygen atoms is $-1$ each.
Oxygen atom that has a double bond with Chromium has oxidation state $+2$
Overall charge on $Cr{O}_5$ is $0$
Let the oxidation state of $Cr$ be $x$
$x+(4\times (-1\left)\right)+(1\times (-2\left)\right)=0x=+6$
$\therefore$ oxidation state of $Cr$ in $Cr{O}_5$ is $+6$