The correct statement(s) regarding the standard electrode potential, E° are
(A) The standard electrode potential changes with the change in the concentration of electrolytes
(B) The standard electrode potential is always zero at 273 K
(C) The concentration of each ion in the solution is unity.
(D) All the gases involved are at 1 bar
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (C) and (D) only
The standard electrode potential, E°, is the electrode potential measured when every species in the half-cell is in its standard state: each ion in solution at unit concentration (1 M), each gas at 1 bar, and solids and liquids pure. The temperature is normally taken as 298 K. E° is therefore a fixed value for a given couple at a given temperature. The potential under any other conditions, E, follows from E° through the Nernst equation; for \( \ce{M^{n+}(aq) + ne^- -> M(s)} \):
\( \displaystyle E = E^{\circ} - \frac{2.303RT}{nF}\log\frac{1}{[\ce{M^{n+}}]} \)
(A) The standard electrode potential changes with the change in the concentration of electrolytes — Incorrect. It is E, not E°, that changes with concentration. E° refers to unit concentration by definition.
(B) The standard electrode potential is always zero at 273 K — Incorrect. Only the standard hydrogen electrode is assigned zero, by convention, at all temperatures. Other couples have their own values, for example +0.34 V for \( \ce{Cu^2+/Cu} \) and −0.76 V for \( \ce{Zn^2+/Zn} \) at 298 K.
(C) The concentration of each ion in the solution is unity. — Correct. Unit concentration of every ion is one of the standard conditions.
(D) All the gases involved are at 1 bar — Correct. A gas is in its standard state at 1 bar, as in the standard hydrogen electrode, Pt(s) | H2(g, 1 bar) | H+(aq, 1 M).
NCERT (2026-27 edition):
Galvanic Cells – “… A potential difference develops between the electrode and the electrolyte which is called electrode potential. When the concentrations of all the species involved in a half-cell is unity then the electrode potential is known as standard electrode potential.”