Determine whether which of the following redox reactions will occur spontaneously in the forward direction?
a) Ni(s) + Zn²⁺(aq) → Ni²⁺(aq) + Zn(s)
b) Fe(s) + Pb⁴⁺(aq) →   Fe²⁺(aq) + Pb(s)
c) Al(s) + Ag⁺(aq) →  Al³⁺(aq) + Ag(s)
d) Pb(s) + Mn²⁺ (aq) → Pb²⁺(aq) + Mn(s)

• A. Only b)
• B. Both b) and c)
• C. a), b) and c)
• D. Both c) and d)

Answer: (B)

Verified step by step guidance

1. Identify the half-reactions for each redox reaction. For example, in reaction a), the oxidation half-reaction is Ni(s) → Ni²⁺(aq) + 2e⁻ and the reduction half-reaction is Zn²⁺(aq) + 2e⁻ → Zn(s).
2. Determine the standard reduction potentials (E°) for each half-reaction using a standard reduction potential table. The more positive the E° value, the greater the tendency for the species to be reduced.
3. Calculate the standard cell potential (E°cell) for each reaction by using the formula: E°cell = E°(reduction) - E°(oxidation).
4. Evaluate the spontaneity of each reaction. A positive E°cell indicates that the reaction is spontaneous in the forward direction.
5. Compare the calculated E°cell values for each reaction to determine which reactions are spontaneous. The reactions with positive E°cell values will occur spontaneously in the forward direction.