Which of the following is used as an electrode in the conductivity cell?

Platinized platinum

The correct answer is (3) platinized platinum.
A platinized platinum electrode is a type of electrode commonly used in various electrochemical applications, especially in conductivity measurements and other analytical techniques. It consists of a platinum substrate that has been coated with a thin layer of finely divided platinum black. This platinized surface provides several advantages and features that make it well-suited for conducting electrical current and facilitating electrochemical reactions in solutions.

Here's a more detailed explanation of the key aspects and advantages of a platinized platinum electrode:

1. Platinum Substrate: The core of the platinized platinum electrode is a solid piece of platinum metal, known for its excellent electrical conductivity, chemical stability, and resistance to corrosion. Platinum is widely used in electrochemistry due to its inert nature and ability to withstand harsh chemical environments.

2. Platinum Black Coating: The platinum substrate is coated with a layer of platinum black. Platinum black is essentially a finely divided form of platinum with a high surface area. The increased surface area is achieved through the deposition of platinum particles, forming a porous and rough texture. This greatly enhances the electrode's active surface area, allowing for improved electrochemical performance.

3. Increased Surface Area: The primary advantage of platinized platinum electrodes lies in their increased surface area compared to a smooth platinum electrode. The higher surface area provides more sites for electrochemical reactions to occur, making the electrode highly sensitive to changes in the electrochemical system being studied.

4. Catalytic Activity: The rough surface and high surface area of platinum black impart catalytic activity to the platinized platinum electrode. This catalytic property facilitates various electrochemical reactions, including redox reactions, which are essential for measurements in electrochemical cells.

5. Lower Overpotential: Overpotential refers to the excess voltage needed to drive an electrochemical reaction at an electrode. The platinized platinum electrode exhibits a lower overpotential due to its catalytic nature, making it more efficient in promoting electrochemical reactions and reducing the energy required for these reactions to occur.

6. Stability and Longevity: The platinum black coating enhances the electrode's stability and extends its operational life. The rough surface prevents the platinum black from easily detaching from the platinum substrate during use, maintaining the electrode's performance over time.

7. Applications: Platinized platinum electrodes find numerous applications in electroanalytical techniques, including conductivity measurements, voltammetry, coulometry, amperometry, and electrochemical impedance spectroscopy. They are widely used in scientific research, industrial processes, and environmental monitoring due to their reliability and accuracy in detecting and quantifying various chemical species in solution.

Overall, the platinized platinum electrode is a crucial tool in electrochemistry, offering increased sensitivity, catalytic activity, and stability for a wide range of electrochemical experiments and analyses. Its unique properties make it an indispensable component in conductivity cells and many other electrochemical applications.