#### Which of the following is a redox reaction? Option 1) Option 2) Option 3) Option 4)

As we learnt in

Redox Reaction -

Redox reaction as a class of reactions in which oxidation and reduction reactions occur simultaneously.

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and,

Oxidation Number -

Oxidation number denotes the oxidation state of an element in a compound ascertained according to a set of rules formulated on the basis that electron pair in a covalent bond belongs entirely to more electronegative elements.

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In a Redox Reaction,  the oxidation states of the constituents should change.

Keeping that in mind, let us look at each reaction:

Clearly, there is no change in the oxidation states.

Clearly, there is no change in the oxidation states.

Clearly, there is no change in the oxidation states.

Finally ,

Clearly, there is a change in the oxidation status of the constituents.

The last reaction is redox.

The oxidation states show a change only in reaction (d).

Option 1)

This option is incorrect.

Option 2)

This option is incorrect.

Option 3)

This option is incorrect.

Option 4)

This option is correct.