ammonia係咪reducing agent黎架??

Ammonia is a weak reducing agent.
(Note that the oxidation numbers of N in both NH3 and NH4+ are -3, and therefore the conversion of NH3 to NH4+ is NOT redox.)

There are some examples in which NH3(g) acts as a reducing agent. The three below are common ones.

1.
Although ammonia gas cannot burn in air, it can burn in pure oxygen with a yellow flame.
4NH3(g) + 3O2(g) → 2N2(g) + 6H2O(g)
The oxidation number of N increases from -3 to 0.

2.
In the presence of red hot platinum as a catalyst, ammonia gas would be oxidized to nitrogen monoxide gas.
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
The oxidation number of N increases from -3 to +2.

3.
Ammonia gas can reduce heated copper(II) oxide to copper.
2NH3(g) + 3CuO(s) → 3Cu(s) + N2(g) + 3H2O(g)
The oxidation number of N increases from -3 to 0.

ammonia係咪reducing agent黎架??
yes, because it has lone pair of electron, which can "lost" to others and thus ammonia (O.N. = 0) oxidized to ammonium ion (O.N. = +1). Therefore, ammonia is reducing agent. (remember, reducing agent, itself oxidized!)