Question

which one of the following reagents is capable of reducing Cu2+ (1M) to Cu(s)?

a) I-(1M) b) Ni(s) c) Al3+ (1M) d) F-(1M) e) Ag(s)

Answer 1

You can definitely exclude c, since Al3+ cannot lose more electrons in order to reduce Cu(2+) to Cu(0)
As for the rest...
Cu(2+) will react with the reagent for which the standard reduction potential (E0) is smaller than the one for Cu(2+) +2e-> Cu(0).
Cu(2+) +2e -> Cu(0) E0=+0.3419 Volt
Ni(+2) + 2e -> Ni(0) E0=-0.257 Volt
I2 + 2e-> 2I- E0=+0.5355 Volt
F2+ 2e-> 2F- E0=+2.866 Volt
Ag(+) + e-> Ag E0=+0.799 Volt

So yes nickel is the correct answer