Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions :
a) `2AgBr(s)+C_(6)H_(6)O_(2)(aq)to2Ag(s)+2HBr(aq)+C_(6)H_(4)O_(2)(aq)`
b) `HCHO(l)+2[Ag(NH_(3))_(2))^(+)(aq)+3OH^(-)(aq)to2Ag(s)+HCOO^(-)(aq)+4NH_(3)(aq)+2H_(2)O(l)`
c) `HCHO(l)+2Cu^(2+)(aq)+5OH^(-)(aq)toCu_(2)O(s)+HCOO^(-)(aq)+3H_(2)O(l)`
d) `N_(2)H_(4)(l)+2H_(2)O_(2)(l)toN_(2)(g)+4H_(2)O(l)`
e) `Pb(s)+PbO_(2)(s)+2H_(2)SO_(4)(aq)to2PbSO_(4)(s)+2H_(2)O(l)`

Explanation

A substance which undergoes oxidation acts as a good reducing agent while the one which undergoes reduction acts as a good oxidising agent.
a) Oxidising agent is AgBr and reducing agent is `C_(6)H_(6)O_(2)`.
Oxidising agent is ammonical silver nitrate (Tollen's reagent) while reducing agent is HCHO.
`Cu^(2+)` undergoes reduction. So it is oxidising agent HCHO undergoes oxidation. So it is reducing agent.
d) Nitrogen in `N_(2)H_(4)` undergoes oxidation. So it is reducing agent.
`H_(2)O_(2)` undergoes reduction. So it is oxidising agent.
e) Pb undergoes oxidation. So is is reducing agent. `PbO_(2)` undergoes reduction. So it is oxidising agent.