Measurement units — The standard redox potential of a substance under biochemical standard conditions (E°') is expressed in which unit?

Introduction / Context:
Redox potentials quantify the tendency of a chemical species to be reduced or oxidized and are essential for predicting electron flow and calculating free-energy changes in bioenergetics. Correct units ensure proper interpretation and use in equations that relate E°' to ΔG°'.

Given Data / Assumptions:

• E°' is an electrical potential difference measured relative to a reference electrode at pH 7.
• Potential relates to energy per unit charge.
• ΔG°' = −n * F * ΔE°' (n = number of electrons; F = Faraday constant).

Concept / Approach:
Because E°' is an electrical potential, its SI unit is the volt (V). Current (ampere), resistance (ohm), or energy (joule) are related electrical quantities but do not describe potential directly. Stating E°' without units is incorrect.

Step-by-Step Solution:

Verification / Alternative check:
Standard biochemical tables list redox couples with potentials in volts or millivolts; conversions to free energy use the relationship above, reinforcing unit correctness.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing potential with energy; forgetting that reported biochemical potentials are adjusted to pH 7 (hence the double prime).

Final Answer:
Volt (V).