Question

What must be added to the following half-reaction for it to be balanced? Al^3+ --> Al




a. 1 electron to the left side
b. 1 electron to the right side
c. 3 electrons to the left side
d. 3 electrons to the right side
e. 3 electrons to both sides

Answer 1

c. 3 electrons to the left side

Reason: Al^3+ is reduced to Al (0), so it must gain 3 electrons: Al^3+ + 3 e^- → Al.