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Question

Oxidation state of Cr in K2Cr2O7 is


A

+6

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B

-7

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C

+2

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D

-2

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Solution

The correct option is A

+6


The oxidation number of oxygen is -2 in most of its compounds , except in peroxides like H2O2, BaO2 etc. where it is -1

1.Another interesting exception is found in the compound OF2 (oxygen difluoride) where the oxidation number of oxygen is +2

2.This is due to the fact that fluorine being the most electronegative element known has always an oxidation number of -1.

3. In compounds formed by union of metals with non-metals, the metal atoms will have positive oxidation numbers and the non-metals will have negative oxidation numbers.

4. The oxidation number of alkali metals (Li, Na, K etc.) is always +1 and those of alkaline earth metals (Be, Mg, Ca etc) is +2.

Therefore, O.N. (O) = -2

O.N. (K) = +1 (alkali metal)

K2Cr2O7 2×(1) +2×n + 7×(-2) = 0

n =6


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