Question

The oxidation number of Cr in $Cr{O}_5$ is _______

• A. +5
• B. +6
• C. +4
• D. +1

Answer 1

The correct option is B +6

Let oxidation number of Cr be 'x'.
Four oxygen atoms are attached to Cr through single bond. Hence, oxidation state of the oxygen atom, in this case, is -1
Another oxygen atom is attached through double bond and this has oxidation number -2.
We know that the sum of all oxidation numbers turns up to be 0
Therefore, $x+(-2)+4(-1)=0$
$x=+6$
Oxidation number of Cr = +6