The value of standard electrode potential of SHE (Standard Hydrogen Electrode) is:

Question

Accepted Answer

The correct option is (4):

The Standard Hydrogen Electrode (SHE) serves as the universal reference electrode in electrochemistry for measuring standard electrode potentials of other electrodes. By international convention, the standard electrode potential of the Standard Hydrogen Electrode (SHE) is arbitrarily assigned a value of exactly zero volts at all temperatures. This convention allows for a consistent scale to determine and compare the reduction potentials of various half-cells. The half-reaction at the SHE is represented as:

$\mathrm{2H^+ (aq, 1 M) + 2e^- \rightleftharpoons H_2 (g, 1 atm)}$

When any other electrode is coupled with the SHE, the measured potential difference (electromotive force, EMF) of the resulting cell directly gives the standard electrode potential of that other electrode. This is a fundamental concept in electrochemistry, essential for understanding galvanic cells, electrolytic cells, and Gibbs free energy calculations.

The incorrect option is (1): The value $\mathrm{-0.74\ V}$ is typically associated with the standard reduction potential of an electrode like the $\mathrm{Cr^{3+}/Cr}$ half-cell, not the SHE.

The incorrect option is (2): The value $\mathrm{0.34\ V}$ is the standard reduction potential of the copper electrode ($\mathrm{Cu^{2+}/Cu}$) when measured against the SHE.

The incorrect option is (3): The value $\mathrm{0.25\ V}$ does not correspond to the standard electrode potential of the SHE. It might be close to the standard reduction potential of some other metal electrodes, such as nickel ($\mathrm{Ni^{2+}/Ni}$) which is $\mathrm{-0.25\ V}$, but it is not the SHE.