Which is not true for a standard hydrogen electrode?

It contains a metallic conductor which does not absorb hydrogen

The correct answer is option 4. It contains a metallic conductor which does not absorb hydrogen.

Let us look at why option (4) is not true:

To determine the correctness of this statement, let's break down the components and characteristics of the Standard Hydrogen Electrode (SHE):

Structure of SHE:

The SHE consists of a platinum electrode that is typically coated with platinum black. Platinum is chosen for its inertness and stability under electrochemical conditions.

The platinum black surface provides a large area for the adsorption and dissociation of hydrogen molecules.

Functionality:

The SHE facilitates the determination of electrode potentials (E°) of other half-reactions by providing a reference point (E° = 0 V).

It operates based on the half-reaction \( 2H^+ + 2e^- \rightarrow H_2 \), where hydrogen ions (protons) in solution are reduced to hydrogen gas at the platinum electrode.

Absorption of Hydrogen:

Platinum does not absorb hydrogen gas in the sense of forming solid solutions or alloys with hydrogen. However, hydrogen atoms or molecules can adsorb onto the platinum surface during the hydrogen evolution reaction. The platinum black coating increases the surface area, enhancing the adsorption of hydrogen atoms and facilitating the redox process involving \( H^+ \) ions.

Conclusion:

Based on the function and structure of the Standard Hydrogen Electrode (SHE), option (4) is indeed correct because the platinum electrode does allow for the adsorption of hydrogen atoms or molecules onto its surface during the redox process. Therefore, I apologize for the oversight earlier. The correct answer is: (4) It contains a metallic conductor which does not absorb hydrogen.

This statement accurately reflects the nature of the platinum electrode in the SHE.