What Determines Oxidizing and Reducing Agents in Redox Reactions?

[yuuri14]

balance the following oxidation reduction reactions. which is the oxidizing agent? reducing agent?
()my answer as balance

a) P4 + Cl2 =(4)PCl5 reducing agent P, o agent Cl
b) Sn2+ + Cu2+ = Sn4+ + Cu+ reducing agent Sn, o agent Cu
c)(2)Cu + H+ +NO3 - = Cu2 + NO2 +H20 " No3, " Cu
D) BR2+ (2)SO2 + H2O = (2)H+ (2)Br- + So4 2- " SO, " Br
e) H2SO4 + 2HBr = SO2 +Br2 + (2) H2O " HBr, " H2SO4

 

[chemisttree]

balance the following oxidation reduction reactions. which is the oxidizing agent? reducing agent?
()my answer as balance

a) P4 + Cl2 =(4)PCl5 reducing agent P, o agent Cl

not balanced

b) Sn2+ + Cu2+ = Sn4+ + Cu+ reducing agent Sn, o agent Cu

charges not balanced

I'm not sure how to make out the rest of them. Perhaps you could rewrite them in a more standard form?