The standard electrode potential of copper is positive. Which of the following statements is true?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Cu is oxidized by nitrate ion in nitric acid
Note: The given answer is as per the official NTA Answer Key. However, there is more than one correct option for this question, as explained below.
E°(\( \ce{Cu^{2+}} \)/Cu) = +0.34 V is positive, so Cu2+ ions are reduced more easily than H+ ions. The reverse process cannot occur: \( \ce{H^{+}} \) ions cannot oxidise Cu. Copper therefore does not dissolve in HCl. In nitric acid, copper dissolves because it is oxidised by the nitrate ion (\( \ce{NO3^{-}} \), E° about +0.96 V), not by \( \ce{H^{+}} \):
\( \ce{Cu -> Cu^2+ + 2e-} \) (×3)
\( \ce{NO3- + 4H+ + 3e- -> NO + 2H2O} \) (×2)
\( \ce{3Cu + 8H+ + 2NO3- -> 3Cu^2+ + 2NO + 4H2O} \)
The other options
Option (1) H+ ions get reduced more easily than Cu2+ ions — Incorrect. The reverse is true; E°(\( \ce{Cu^{2+}} \)/Cu) = +0.34 V is higher than E°(\( \ce{H^{+}} \)/\( \ce{H2} \)) = 0.00 V.
Option (2) Cu does not dissolve in HCl — Is also correct. Hydrogen ions cannot oxidise Cu, so copper does not dissolve in HCl; the book states it in the same passage.
Option (4) H+ ions cannot reduce copper — Incorrect. Metallic copper is not reduced by anything; the process in question is the oxidation of Cu, which \( \ce{H^{+}} \) cannot bring about. The statement names the wrong process.
NCERT (2026-27 edition):
Electrode Potential – …
