Question

The formal oxidation numbers of $Cr$ and $Cl$ in the ions $C{r}_2{O}_7^{2-}$ and $Cl{O}_3^{-}$, respectively are

• A. + 6 and +7
• B. +7 and +5
• C. +6 and +5
• D. +8 and +7

Answer 1

Answer: (C)

In $C{r}_2{O}_7^{2-}$
Let the oxidation state of $Cr$ be $x$
$\therefore 2(x)+7(-2)=-2$
$2x-14=-2$
$2x=12$
$x=+6$
In $Cl{O}_3^{-}$,
Let the oxidation state of $Cl$ be $x$
$\therefore 1(x)+3(-2)=-1$
$x-6=-1$
$x=+5$