"(b) a redox reaction"
"(c) a comproportionation reaction".
(aq) simply means the "aquated ion", or the ionic species in aqueous solution. For Cu(SO_4)(aq) this means Cu^(2+) and SO_4^(2-), where in aqueous solution Cu^(2+) exists as the coordination complex [Cu(OH_2)_6]^(2+), which has a truly beautiful blue colour.
In "(c)", this is a subset of redox reaction, but here, instead of one species being reduced, and another species oxidized, which conventionally occurs, as for "(b)", here the reactants are in different oxidations states, i.e. N^(-III) in "ammonia", and N^(+I) in "dinitrogen monoxide" (note that we could formally assign oxidation states of N^0, and N^(+II) but the average oxidation is N^(+I)), these formally exchange electrons so that their product gives N^(+I), a formal [comproportionation.](https://en.wikipedia.org/wiki/Comproportionation)
I assume you are a first/second year undergrad. If you are an A-level student you don't need to know about "comproportionation".
