Arrange the given metals in the increasing order of their reducing powers
(A) Ag+/Ag = 0.80V
(B) Hg2+/Hg = 0.79 V
(C) Mg2+/Mg = −2.37V
(D) Cr3+/Cr = −0.74V
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B), (D), (C)
A reducing agent gives away electrons, i.e. it is itself oxidised. The standard reduction potential E° measures the tendency of the ion to take electrons back. So the lower (more negative) the E°, the more easily the metal loses electrons and the stronger it is as a reducing agent.
Arranging the given values from the highest to the lowest E°:
\( \displaystyle \mathrm{Ag}\ (+0.80\ \mathrm{V})>\mathrm{Hg}\ (+0.79\ \mathrm{V})>\mathrm{Cr}\ (-0.74\ \mathrm{V})>\mathrm{Mg}\ (-2.37\ \mathrm{V}) \)
Reducing power follows the reverse of this order:
(A) Ag: E° = +0.80 V, the weakest reducing agent
(B) Hg: E° = +0.79 V
(D) Cr: E° = −0.74 V
(C) Mg: E° = −2.37 V, the strongest reducing agent
Shortcut: Mg, with the most negative E°, must come last and Ag, with the most positive E°, first. Only Option (1) starts with (A) and ends with (C).
NCERT (2026-27 edition):
Measurement of Electrode Potential – …
