How do you solve this

Question

Are any of these equations redox reactions? if so what are their reducing and oxidizing agents?

CuSO₄(aq)+Zn(s)→ZnSO₄(aq)+Cu(s)

HCl(aq)+NH₃(aq)→NH₄Cl(aq)

2Ca(s)+O₂(g)→2CaO(s)

Answer 1

You solve it by checking the formal charges of the atoms on both sides of the arrow. If there is a change, then it is a redox. The thing oxidized has it formal charge go from a lower value to higher value.