What are the reducing and oxidizing agents in these equations

a)Ca(s) + Cl2(g) -> CaCl2(s)

b) Cl2(g) + H2S(g) -> HCl(g) + S(s)

c) Ba(NO3)2(aq) + Na2SO4(aq) -> BaSO4(s) + 2NaNO3(aq)

d) CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)

e) Ca(OH)2(aq) + CO2(g) -> CaCO3(s) + H2O(l)

f) Ni(s) + CuSO4(s) -> NiSO4(aq) + Cu(s)

g) Cl2O7(g) + H2O(l) -> 2HClO4(aq)

h) 2CuCl(aq) -> CuCl2(aq) + Cu(s)

It helps to look at the oxidation numbers of the elements.

a) Ca(s) + Cl2(g) --> CaCl2(s)
Ca goes from 0 to +2 ---> undergoing oxidation --> Ca is the reducing agent.
Cl goes from 0 to -1 ---> undergoing reduction --> Cl is the oxidizing agent.
I know it's confusing but the substance undergoing oxidation is the reducing agent, and the substance undergoing reduction is the oxidizing agent.

b) Cl2(g) + H2S(g) --> HCl(g) + S(s)
Cl goes from 0 to -1 --> undergoing reduction --> Cl2 is the oxidizing agent.
S goes from -2 to 0 --> undergoing oxidation --> H2S is the reducing agent.

c) This is a trick question, as none of the elements are changing oxidation state. In fact, this is a metathesis reaction.

d) CH4(g) + 2 O2(g) --> CO2(g) + 2 H2O(l)
C goes from -4 to +4 --> undergoing oxidation --> CH4 is the reducing agent.
O goes from 0 to -2 --> undergoing reduction --> O2 is the oxidizing agent.

e) Another trick question. This is an acid-base reaction.

f) Ni goes from 0 to +2 --> Ni is the reducing agent.
Cu goes from +2 to 0 --> CuSO4 is the oxidizing agent.

g) No element changes its oxidation state here.

h) 2CuCl(aq) --> CuCl2(aq) + Cu(s)
Cu goes from +1 to +2 AND to 0. Here half the CuCl is being oxidized (to CuCl2) and half is being reduced (to Cu). So CuCl is both the reducing agent and the oxidizing agent.