Justify that the following reaction are redox reactions:
a. `CuO(s)+H_(2)(g)rarr Cu(s)+H_(2)O(g)`
b. `Fe_(2)O_(3)(s)+3CO(g)rarr 2Fe(s)+3CO_(2)(g)`
c. `4BCl_(3)(g)+3LiAlH_(4)(s) rarr 2B_(2)H_(6)(g)+3LiCl(s)+3AlCl_(3)(s)`
d. `2K(s)+F_(2)(g)rarr 2K^(o+)F^(Θ)(s)`
e. `4NH_(3)(g)+5O_(2)(g)rarr 4NO(g)+6H_(2)O(g)`

Explanation

(a) `overset(+2)(Cu)overset(-2)O(s)+overset(0)H_2(g)rarroverset(0)Cu(s)+overset(+1)(H_2)overset(-2)O(g)`
In this case, O.N. of Cu decreases from +2 (in CuO) to 0 (in Cu) and that of H increase from 0 (in `H_2` ) to +1 (in `H_2O` ) . Therefore , CuO is reduced to Cu while `H_2` is oxidused to `H_2O` . Thus, this is a redox reaction.
(b) `overset(+3)(Fe_2)overset(-2)O_3+overset(+2-2)(3CO)rarr2overset(0)Fe(s)+overset(+4-2)(3CO_2)`
O.N. of Fe decreases from +3 (in `Fe_2O_3` ) to 0 (in Fe) and that of C increases from +2 (in CO) to +4 (in `CO_2` ) . Therefore , `Fe_2O_3` is reduced while CO is oxidised Thus , this is a redox reaction.
(c) `4overset(+3)Boverset(-1)(Cl_3(s))+overset(+1)(3Li)overset(+3)(Al)overset(-1)H_4(s) rarroverset(-3)(2B_2)overset(+1)(H_6)(g)+overset(+1)(3Li)overset(-1)(Cl)(s)+overset(+3-1)(3AlCl_3(s))`
O.N . of B decreases form +3 (in `BCl_3`) to -3 in `B_2H_6` and that of H increases from -1 (in `LiAlH_4`) to +1 (in `B_2H_6` ) . Therefore , `BCl_3` is reduced and `LiAIH_4` is oxidised . Hence , it is a redox reaction.
(d) `2overset(0)K(s)+overset(0)F_2(g)rarr2overset(+1)(K^+)+overset(-1)(F^(-))(s)`
O. N. of K increases from 0 (in K) to +1 (in `K^(+)` ) and that of F decreases from 0 in `(F_2)` to - 1 (in `F^(-)`) . Hence , K has been oxidised while `F_2` has been reduced . Therefore , it is a redox reaction.
(e) `4overset(-3)Noverset(+1)(H_3)(g)+5overset(0)O_2(g) rarroverset(+2-2)(4NO)(g)+overset(1)(6H_2)overset(-2)O(g)`
In this case O.N. of the increases from - 3 (in `NH_3`) to +2 (in NO) and that of O decreases from 0 (in `O_2` ) to -2 (in `H_2`) . Therefore , `NH_3` has been oxidised while `O_2` has been reduced . Hence , it is a redox reaction.