Which of the following is an oxidation-reduction reaction?
a.) fe2o3 + 3co -> 2fe + 3co2
b.) cuso4 + 2naoh -> cu(oh)2 +na2so4
c.) 2naoh + h2co3 -> na2co3 + 2naoh
d.) pb(no3)2 + na2so4 -> 2nano3 + pbso4

The correct answer is Option a.

Explanation:

Oxidation-reduction reaction or redox reaction is defined as the reaction in which oxidation and reduction reactions occur simultaneously.

Oxidation reaction is defined as the reaction in which a substance looses its electrons. The oxidation state of the substance increases.

Reduction reaction is defined as the reaction in which a substance gains electrons. The oxidation state of the substance gets reduced.

For the given options:

Option A:

On reactant side:

Oxidation state of iron = +3

Oxidation state of carbon = +2

On product side:

Oxidation state of iron = 0

Oxidation state of carbon = +4

The oxidation state of iron reduces from +3 to 0, it is getting reduced. Thus, it is getting reduced and it undergoes reduction reaction. The oxidation state of carbon increases from +2 to +4. Thus, it is getting oxidized and it undergoes oxidation reaction.

Thus, it is considered as redox reaction.

Option B:

The above reaction is double displacement reaction because here exchange of ions takes place.

Option C:

The above reaction is a neutralization reaction because an acid reacts with base to produce salt and water.

Option D:

The above reaction is double displacement reaction because here exchange of ions takes place.

Hence, the correct answer is Option A.