NEETChemistryd and f Block Elements
The standard electrode potentials ( E ^ ) for the M ²⁺ / M couple of some 3d series elements are observed as follows: V (-1.18 V ) , Cr (-0.90 V ) , Mn (-1.18 V ) , Fe (-0.44 V ) , Ni (-0.25 V ) , Cu (+0.34 V ) , and Zn (-0.76 V ) . While the general trend across the series is that the E ^ value becomes less negative, Mn and Zn break this trend by exhibiting more negative values than expected. Which of the following
Options
- AMn and Zn have exceptionally high enthalpies of atomisation compared to other transition metals.
- BThe hydration enthalpies of Mn ²⁺ and Zn ²⁺ are exceptionally high, making their formation highly favourable.
- CThe formation of Mn ²⁺ and Zn ²⁺ is thermodynamically favoured due to their stable exactly half-filled (d^5 )
- DMn ²⁺ and Zn ²⁺ achieve stability by attaining d^4 and d^9 electronic configurations respectively.
Correct answer
C. The formation of Mn ²⁺ and Zn ²⁺ is thermodynamically favoured due to their stable exactly half-filled (d^5 )
Step-by-step solution
The standard electrode potential E ^ ( M ²⁺ / M ) depends on the sum of the enthalpy of atomisation, ionisation enthalpies ( _i H ₁ + _i H ₂ ), and hydration enthalpy. Across the 3d series, the general trend is a less negative E ^ value due to the general increase in the sum of the first and second ionisation enthalpies. However, Mn and Zn have more negative E ^ values than the trend predicts. This is because the Mn ²⁺ ion has a stable exactly half-filled 3d^5 configuration, and the Zn ²⁺ ion has a stable fully-fil