a) Balanced equation;
⇒ 
b) oxidizing agent: N
reducing agent: Au
a) The unbalanced redox equation is as follows:
⇒ 
Balance all atoms other than H and O.
⇒ 
The oxidation number of gold changes from 0 to +3. The change in the oxidation number of gold is 3.The oxidation number of nitrogen changes from +5 to +4. The change in the oxidation number of nitrogen is 1.
So,
⇒ 
Now balance O atoms on RHS,
⇒ 
Now, balance hydrogen atoms on RHS,
⇒ 
This is the balanced chemical equation.
b) oxidizing agent: N
reducing agent: Au
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