In 3d series, the metal having the highest M²⁺/M standard electrode potential is :

Solution

Chemistry ma’am · 3 steps

Copper is the only 3d metal with a positive E°(M²⁺/M), so it wins straight away.

1. What the value means. E°(M²⁺/M) measures how much M²⁺ wants to be reduced back to the metal. A more positive value means the metal is harder to oxidise to M²⁺.

   Couple	E° / V	Sign
   Cr²⁺/Cr	-0.91	negative
   Fe²⁺/Fe	-0.44	negative
   Cu²⁺/Cu	+0.34	positive
   Zn²⁺/Zn	-0.76	negative

2. Why copper. Turning Cu into Cu²⁺ in water costs a lot of energy: copper has a high enthalpy of atomisation and a large IE₁ + IE₂. The hydration enthalpy of Cu²⁺ does not make up for this, so the overall change is unfavourable and E° comes out positive.
3. So. Cu has the highest E°(M²⁺/M), +0.34 V. This is also why copper does not liberate H₂ from dilute acids. The answer is (c).

The idea to keep. In the 3d series, only copper has a positive E°(M²⁺/M). The value depends on atomisation, ionisation and hydration energies together, not on one factor alone.

Answer from the NTA final answer key. Solution by PrepWiser.