Which of the following redox reactions do you expect to occur spontaneously in the forward direction under standard conditions?

a. Ni(s)+Zn2+(aq)→Ni2+(aq)+Zn(s)
b. Pb(s)+Mn2+(aq)→Pb2+(aq)+Mn(s)
c. Ni(s)+Pb2+(aq)→Ni2+(aq)+Pb(s)
d. Cr(s)+3Ag+(aq)→Cr3+(aq)+3Ag(s)
e. None of the above

b. spontaneous.

c. spontaneous.

Explanation:

Using the net standard potential, it is possible to determine if the reaction is spontaneous or not.  If the standard potential of the reaction is positive, the reaction is spontaneous, whereas if the standard potential of the reaction is negative, the reaction is non-spontaneous.

a. Ni(s)+Zn2+(aq)→Ni2+(aq)+Zn(s)  E° = - 0.53 v

b. Pb(s)+Mn2+(aq)→Pb2+(aq)+Mn(s)  E° = + 0.10 v

c. Ni(s)+Pb2+(aq)→Ni2+(aq)+Pb(s)  E° = + 2.46 v

d. Cr(s)+3Ag+(aq)→Cr3+(aq)+3Ag(s) E° = - 1.05 v

the answer is b. dilution