The oxidation number of Cr in K_2 Cr_2 O_7 is :

MCQ

The oxidation number of $\text{Cr}$ in $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ is :

A
$+3$
B
$−3$
✓
$+6$
D
$−6$

✓

Answer

Correct option: C.

$+6$

The sum of the oxidation numbers in a polyatomic ion is equal to the charge on the ion.
The oxidation number of simple ions is equal to the charge on the ion.
The metals in Group $\text{IA (K)}$ atom has an oxidation number of $+1$.
Oxygen usually has an oxidation number of $−2.$
Oxidation no of $\text{Cr}$ in $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$
$=2\times 1+2\times \text{x}+7\times (−2)=0$
$\text{x}=\frac{14-2}{2}=+6$

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