Which reference electrode has a standard potential closest to +0.197 V relative to the SHE?

• A. Ag/AgCl (saturated KCl) E° ≈ +0.197 V relative to SHE.
• B. SCE (saturated calomel electrode) E° ≈ +0.241 V relative to SHE.
• C. Hg/Hg2Cl2 E° ≈ +0.56 V relative to SHE.
• D. SHE E° ≈ 0 V.

Answer: (A)

Standard potentials are given relative to the standard hydrogen electrode (SHE), so you compare each reference’s E° directly to +0.197 V. The silver/silver chloride reference in saturated KCl has E° about +0.197 V vs SHE, which matches the target value. The saturated calomel electrode sits around +0.241 V, a bit more positive, while the mercury/mercury(I) chloride electrode is about +0.56 V, much farther away. The SHE itself is defined as 0 V. So the silver/silver chloride reference is the closest to +0.197 V.