The following half cell represents, normal hydrogen electrode (NHE) :
Pt|H+ (1M HCl)|H2(g) (1 atm)
The question asks specifically for the normal hydrogen electrode, and the distinction between NHE and SHE is exactly what it is testing. The two are often used loosely as synonyms, but they are defined differently.
The SHE (standard hydrogen electrode) is the rigorous thermodynamic reference. It requires hydrogen ion activity equal to 1, \(a_{H^{+}} = 1\), together with H2 at unit fugacity. Activity is the thermodynamically effective concentration, \(a = \gamma c\), and because interionic attractions make \(\gamma < 1\) in any real solution, unit activity is a hypothetical ideal state rather than something poured from a bottle.
The NHE (normal hydrogen electrode) is the older, practical version defined on a concentration basis — a 1 normal (1 M) acid solution, conventionally 1 M HCl, with hydrogen at 1 atm over a platinised platinum electrode. Being defined by concentration rather than activity, it is realisable in the laboratory, and its potential differs from the SHE by only a few millivolts.
So the option written in terms of \(a = 1\) describes the SHE, not the NHE, and is the correct answer to a different question.
Among the concentration-based options, hydrochloric acid is the right choice because it is a strong monoprotic acid, fully dissociated, so a 1 M solution really does deliver 1 M H+.
1 M H2SO4 fails because it is diprotic: the first ionisation is complete but the second is not, so the hydrogen ion concentration is neither 1 M nor well defined.
1 M H3PO4 fails because it is a weak triprotic acid, only partly dissociated, giving far less than 1 M H+.
The platinised platinum serves as an inert, high-surface-area catalyst for the H+/H2 equilibrium rather than taking part in the reaction.
Hence the NHE is Pt|H+ (1M HCl)|H2(g) (1 atm).
Similar Questions
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Which of the following statement is incorrect ?
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E°(MnO4-) = +1.51 V
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Important Questions from Thermodynamics
- Second law of thermodynamics states that
A. Energy flows from higher concentration to lower concentration.
B. Order becomes disorder during energy transformations.
C. The quality of energy degrades as it is transformed.
D. Degraded energy is entropy, dessipated as waste products or heat.
E. Enthalpy is wasted in energy transformation.
Choose the most appropriate answer from the options given below: Choose the Incorrect Statement:
1 For a system at equilibrium, chemical potential is same in all phases.
2 Gibb's free energy change is zero at equilibrium state of a system.
3 Gibb's free energy change is positive for reaction to occur spontaneously.
4 $\Delta G$ will become more negative with increasing temperature.- In a closed thermodynamic system, across its boundaries
Melting Point of pure ice is-
Which one among the following statements with reference to the properties of water is not correct?
