A galvanic cell consists of one half cell that is made up of an inert graphite electrode in a solution containing 1.0 M Fe$^{2+}$(aq) and 1.0 M Fe$^{3+}$(aq) at 25$^{ ext{C}}$ - VCE - SSCE Chemistry - Question 8 - 2005 - Paper 1

To determine which electrode can serve as the second half cell while ensuring the electrode polarity is positive, we need to understand the roles of the electrodes in a galvanic cell. The half-cell with the higher reduction potential will act as the cathode, and this is where the reduction occurs.

1. Check the Half-Cells: We compare the standard reduction potentials of the options given:

   • Lead (Pb$^{2+}$): Lead has a reduction potential that is relatively low, resulting in a weaker tendency to be reduced.
   • Silver (Ag$^{+}$): Silver has a higher standard reduction potential, making it a good candidate for the cathode in the galvanic cell.
   • Iron (Fe$^{2+}$): While iron can be reduced, it does not have a higher potential compared to silver.
   • Inert Graphite in Br$^{-}$: This option cannot serve as a reducing agent.

2. Conclusion: Since the silver electrode in a solution of 1.0 M Ag$^{+}$(aq) has a higher reduction potential than the other options, it will function as the second half cell with a positive polarity.