J.R. S. answered 04/14/20
Ph.D. University Professor with 10+ years Tutoring Experience
To identify the oxidant (oxidizing agent), you want to find the agent that is reduced. If it is reduced (gains electrons), it will be the oxidant.
For #7, we have...
(a) SO32−(𝑎𝑞)+Cu(OH)2(𝑠) ⟶ SO42−(aq) + Cu(OH)(s) (unbalanced)
....4+...............2+.....................6+................1+............oxidation numbers for S and Cu
S went from 4+ to 6+ so it lost electrons and was oxidized
Cu went from 2+ to 1+ so it gained electrons and was reduced. It is the oxidant as in Cu(OH)2
One more so you get the idea, and the hopefully you can do the others
(b) O2(𝑔) + Mn(OH)2(𝑠) ⟶ MnO2(s) + 2H2O (unbalanced)
.....0..............2+........................4+...2- ..........oxidation numbers for oxygen and Mn
O goes from zero to 2- so it is reduced making it the oxidant. This would be in basic
Too many in # 6 to do, but will do one so you get the idea... After running through it, you'll see why there are too many for me to do,..In fact this answer is too long and it won't let me post all of it. I'll try adding the rest to the comments or another of your quesitons.

Rosa B.
thank you !04/14/20
J.R. S.
04/14/20