Answer the question on the basis of passage given below:
For the Transition Elements.
|
|
Sc |
Ti |
V |
Cr |
Mn |
Fe |
Co |
Ni |
Cu |
Zn |
|
Atomic Number: |
21 |
22 |
23 |
24 |
25 |
26 |
27 |
28 |
29 |
30 |
Which transition metal ion, \(M^{2+}/M\), has standard electrode potential \(E^\circ = +0.34\ V\)?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Cu
Among the first-row transition metals, copper is the only one with a positive E°(M2+/M), +0.34 V. The energy needed to turn Cu(s) into Cu2+(aq) (a high enthalpy of atomisation plus the first two ionisation enthalpies) is not balanced by the hydration enthalpy of \( \ce{Cu^2+} \). That is why copper does not liberate hydrogen from dilute acids; Mn, Co and Zn all have negative values.
NCERT (2026-27 edition):
Trends in the M2+/M Standard Electrode Potentials – “… The unique behaviour of Cu, having a positive E°, accounts for its inability to liberate H2 from acids. Only oxidising acids (nitric and hot concentrated sulphuric) react with Cu, the acids being reduced. The high energy to transform Cu(s) to Cu2+(aq) is not balanced by its hydration enthalpy.”