Question

Oxidation numbers of P in $P{O}_4^{3-}$, of S in $S{O}_4^{2-}$ and that of Cr in $C{r}_2{O}_7^{2-}$ are respectively:

• A. +3,+6 and +5
• B. +5,+3and +6
• C. -3,+6 and +6
• D. +5,+6 and +6

Answer 1

The correct option is D +5,+6 and +6

(I) ${}^{x}P{O}_4^{3-}\Rightarrow x+4\times (-2)=-3$

$\Rightarrow x=-3+8=+5$

$\Rightarrow x=+5$

Oxidation number of $P=+5$

(II) ${}^{x}S{O}_4^{2-}\Rightarrow x+4\times (-2)=-2$

$\Rightarrow x=-2+8$

$\Rightarrow x=+6$

Oxidation number of $S=+6$

(III) ${}^{x}C{r}_2{O}_7^{2-}\Rightarrow 2x+7\times (-2)=-2$

$\Rightarrow 2x=-2+14$

$\Rightarrow 2x=12$

$\Rightarrow x=\frac{12}{2}=+6$