Polarographic Measurement Procedure

Dropping Mercury Electrode (DME)
The correct statement for a polarographic measurement procedure is option 'B', which states that the dropping mercury electrode (DME) is the working electrode.

Working Electrode
In polarography, the working electrode is the electrode at which the electrochemical reaction takes place. It is responsible for capturing the current that is generated during the redox reaction. The DME, also known as the hanging mercury drop electrode (HMDE), is commonly used as the working electrode in polarography.

Mercury Droplet Formation
The DME is created by allowing a small droplet of mercury to form at the tip of a capillary tube. The mercury droplet is then repeatedly dropped onto the working electrode surface. The mercury droplet acts as both the electrode material and the electrolyte, allowing for the electrochemical reactions to occur.

Redox Reactions
During polarographic analysis, the electroactive species in the sample undergoes redox reactions at the surface of the mercury droplet. The redox reactions result in the transfer of electrons between the electroactive species and the mercury electrode.

Current Measurement
The current flowing through the working electrode, known as the diffusion current (Id), is directly proportional to the concentration of the electroactive species in the sample. The current is measured using a potentiostat, which applies a constant potential to the working electrode and measures the resulting current.

Supporting Electrolyte
To minimize the interference from other ions present in the sample, a supporting electrolyte is often added. The supporting electrolyte is a solution that maintains a constant ionic strength and helps to improve the accuracy and precision of the measurement. It does not directly affect the measurement of the diffusion current.

Residual Current
The residual current, also known as the background current, is the current that flows through the working electrode in the absence of any electroactive species. This current can arise from impurities in the sample or other sources of interference. To minimize the residual current, the addition of a supporting electrolyte is often necessary.

Conclusion
In summary, the correct statement for a polarographic measurement procedure is that the dropping mercury electrode (DME) is the working electrode. The DME allows for the electrochemical reactions to occur at its surface, and the resulting diffusion current is measured to determine the concentration of the electroactive species in the sample. The addition of a supporting electrolyte helps to minimize interference and improve the accuracy of the measurement.