JEE Main · 2021 · Shift-IeasyDNF-070

The electrode potential of M2+/M of 3d-series elements shows positive value for:

d & f-Block Elements · Class 12 · JEE Main Previous Year Question

Question

The electrode potential of M2+/M\text{M}^{2+}/\text{M} of 3d-series elements shows positive value for:

Options
  1. a

    Co

  2. b

    Fe

  3. c

    Zn

  4. d

    Cu

Correct Answerd

Cu

Detailed Solution

Standard reduction potentials E°M2+/ME°_{M^{2+}/M} for 3d metals:

| Metal | E°M2+/ME°_{M^{2+}/M} (V) | Positive? | |-------|---------------------|----------| | Co | 0.28-0.28 | No | | Fe | 0.44-0.44 | No | | Zn | 0.76-0.76 | No | | Cu | +0.34+0.34 | Yes ✓ |

Cu is the only first-row transition metal with a positive E°M2+/ME°_{M^{2+}/M} value.

This means Cu²⁺ is more easily reduced to Cu than H⁺ is reduced to H₂ — hence Cu does not dissolve in dilute acids and cannot liberate H₂.

Answer: Option (4) — Cu

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