Answer : The balanced equations involve oxidation-reduction are:
(a) ![2H_2SO_4(aq)+2NaBr(s)\rightarrow Br_2(l)+SO_2(g)+Na_2SO_4(aq)+2H_2O(l)](https://tex.z-dn.net/?f=2H_2SO_4%28aq%29%2B2NaBr%28s%29%5Crightarrow%20Br_2%28l%29%2BSO_2%28g%29%2BNa_2SO_4%28aq%29%2B2H_2O%28l%29)
(b) ![3SO_2(g)+2HNO_3(aq)+2H_2O(l)\rightarrow 3H_2SO_4(aq)+2NO(g)](https://tex.z-dn.net/?f=3SO_2%28g%29%2B2HNO_3%28aq%29%2B2H_2O%28l%29%5Crightarrow%203H_2SO_4%28aq%29%2B2NO%28g%29)
(c) ![NaI(aq)+3HOCl(aq)\rightarrow NaIO_3(aq)+3HCl(aq)](https://tex.z-dn.net/?f=NaI%28aq%29%2B3HOCl%28aq%29%5Crightarrow%20NaIO_3%28aq%29%2B3HCl%28aq%29)
Explanation :
Redox reaction or Oxidation-reduction reaction : It is defined as the reaction in which the oxidation and reduction reaction takes place simultaneously.
Oxidation reaction : It is defined as the reaction in which a substance looses its electrons. In this, oxidation state of an element increases. Or we can say that in oxidation, the loss of electrons takes place.
Reduction reaction : It is defined as the reaction in which a substance gains electrons. In this, oxidation state of an element decreases. Or we can say that in reduction, the gain of electrons takes place.
(a) The given chemical reaction is:
![2H_2SO_4(aq)+2NaBr(s)\rightarrow Br_2(l)+SO_2(g)+Na_2SO_4(aq)+2H_2O(l)](https://tex.z-dn.net/?f=2H_2SO_4%28aq%29%2B2NaBr%28s%29%5Crightarrow%20Br_2%28l%29%2BSO_2%28g%29%2BNa_2SO_4%28aq%29%2B2H_2O%28l%29)
This reaction involve oxidation-reduction reaction because the oxidation state bromine changes from (-1) to (0) which shows oxidation and sulfur changes from (+6) to (+4) which shows reduction.
(b) The given chemical reaction is:
![3SO_2(g)+2HNO_3(aq)+2H_2O(l)\rightarrow 3H_2SO_4(aq)+2NO(g)](https://tex.z-dn.net/?f=3SO_2%28g%29%2B2HNO_3%28aq%29%2B2H_2O%28l%29%5Crightarrow%203H_2SO_4%28aq%29%2B2NO%28g%29)
This reaction involve oxidation-reduction reaction because the oxidation state sulfur changes from (+4) to (+6) which shows oxidation and nitrogen changes from (+5) to (+2) which shows reduction.
(c) The given chemical reaction is:
![NaI(aq)+3HOCl(aq)\rightarrow NaIO_3(aq)+3HCl(aq)](https://tex.z-dn.net/?f=NaI%28aq%29%2B3HOCl%28aq%29%5Crightarrow%20NaIO_3%28aq%29%2B3HCl%28aq%29)
This reaction involve oxidation-reduction reaction because the oxidation state iodine changes from (-1) to (+5) which shows oxidation and chlorine changes from (+5) to (-1) which shows reduction.
(d) The given chemical reaction is:
![PBr_3(l)+3H_2O(l)\rightarrow H_3PO_3(aq)+3HBr(aq)](https://tex.z-dn.net/?f=PBr_3%28l%29%2B3H_2O%28l%29%5Crightarrow%20H_3PO_3%28aq%29%2B3HBr%28aq%29)
This reaction does not involve oxidation-reduction reaction because the oxidation state of element present on reactant and product side are same.