Answer:

Potentiometric methods are analytical techniques that measure the potential difference (voltage) between two electrodes in an electrochemical cell. The indicator electrode is one of the two electrodes in the cell, and it is responsible for sensing the analyte of interest and generating a potential difference.

Among the given options, the metals that can be used as indicator electrodes in potentiometric methods are Ag, Cu, Hg, and Pb. Let's discuss each of these metals in detail:

Ag (Silver):
- Silver is commonly used as an indicator electrode in potentiometric methods.
- It is known for its low reactivity and stable electrical potential, making it suitable for accurate measurements.
- Ag/AgCl electrode is a widely used reference electrode in potentiometric measurements.

Cu (Copper):
- Copper can also be used as an indicator electrode in certain potentiometric methods.
- However, it is less commonly used compared to silver.
- Copper electrodes can be used in specific applications where the analyte interacts with copper ions.

Hg (Mercury):
- Mercury electrodes are commonly used in polarographic methods, which are a type of potentiometric technique.
- These electrodes are particularly useful for determining trace amounts of metal ions.

Pb (Lead):
- Lead electrodes are also used in certain potentiometric methods.
- They are often employed in electroanalytical techniques for the determination of various analytes.

Therefore, the correct answer is option B, which includes Ag, Cu, Hg, and Pb. These metals can be used as indicator electrodes in potentiometric methods. The other options do not include all the metals that are commonly used as indicator electrodes in such techniques.