Question

redox reaction definition

Answer 1

Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a reduction process and a complementary oxidation process, two key concepts involved with electron transfer processes. 
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Answer 2

the reaction in which oxidation and reduction reaction occurs called as redox reaction
for e.g.2H2S +SO2>3S+2H2O
redox reaction is the chemical reaction in which reductant is oxidised by oxidant and is reduced by reductant