Justify that the following reactions are redox reactions.
a) `CuO(s)+H_(2)(g)toCu(s)+H_(2)O(g)`
b) `Fe_(2)O_(3)(s)+3CO(g)to2Fe(s)+3CO_(2)(g)`
c) `4BCl_(3)(g)+3LiAlH_(4)(s)to2B_(2)H_(6)(g)+3LiCl(s)+3AlCl_(3)(s)`
d) `2K(s)+F_(2)(g)to2K^(+)F^(-)(s)`
e) `4NH_(3)(g)+5O_(2)(g)to4NO(g)+6H_(2)O(g)`

Explanation

a) `CuO(s)+H_(2)(g)toCu(s)+H_(2)O(g)`
In this reaction the oxidation number of Cu decreased from +2 to 0 and the oxidation state of `H_(2)` is increased to +1.
So it is a redox reaction.
b) `Fe_(2)O_(3)(s)+3CO(g)to2Fe(s)+3CO_(2)(g)`
In this reaction the oxidation number of Fe ion `Fe_(2)O_(3)` is decreased to zero in Fe from +3 and the oxidation number of carbon in CO is increased from +2 to +4 ion `CO_(2)`. So it is a redox reaction.
c) `4BCl_(3)(g)+3LiAlH_(4)(s)to2B_(2)H_(6)(g)+3LiCl(s)+3AlCl_(3)(s)`
In `LiAlH_(4)`, hydrogen is present as `H^(-)` ion with more negative charge on H. But ion `B_(2)H_(6)` also the H atom will have some negative charge as the electronegativity of H is 2.1 while that of boron iis 2.0.
According to the modern concept decrease electron density is reduction and increase in electron density is oxidation.
Here the electron density decrease at hydrogen and increases at boron because hydrogen and increases at boron because the bond with more electronegative atom (B - Cl) changes to less electronegative atom (B - H). So it is also redox reaction.
d) `2K(s)+F_(2)(g)to2K^(+)F^(-)(s)`
In the formation of `K^(+)F^(-)`, K loses electron (oxidation) and F gains electron (reduction) so it is redox reaction.
e) `4NH_(3)(g)+5O_(2)(g)to4NO(g)+6H_(2)O(g)`
The oxidation of N increases from -3 to +2 in the conversation of `NH_(3)` to NO. It is oxidation.
The oxidation number of `O_(2)` changes from zero to -2.
It is reduction. So it is redox reaction.