Answer:

Step-by-step explanation:
The reaction is called redox reaction if there is oxidation and reduction in the reaction.
Oxidation is gain of oxygen, loss of hydrogen or loss of electrons.
Reduction is gain of hydrogen, loss of oxygen or gain of electrons.
a)

Here Zn is undergoing oxidation and oxygen is undergoing reduction. so it is an oxidation reduction reaction
b) In second reaction , the oxidation state of all elements remained the same. hence no oxidation reduction occur.
c) in third reaction also, the oxidation state of all elements remained the same. hence no oxidation reduction occur.
d) in fourth reaction also,the oxidation state of all elements remained the same. hence no oxidation reduction occur.