Reducing power refers to the ability of a substance to donate electrons (undergo oxidation). This ability is inversely related to the standard reduction potential.
1. Core Principle:
The lower (more negative) the standard reduction potential of an element, the more easily it is oxidized, and consequently, the stronger its reducing power.
2. Comparing the Given Potentials:
• $E^0_A = 0.68\text{V}$ (Highest value) [cite: 74]
• $E^0_B = -2.54\text{V}$ (Lowest/Most negative value) [cite: 74]
• $E^0_C = -0.50\text{V}$ (Intermediate value) [cite: 74]
3. Determining the Order:
Since a lower potential means higher reducing power:
• $B$ ($-2.54\text{V}$) has the highest reducing power[cite: 74].
• $C$ ($-0.50\text{V}$) has intermediate reducing power[cite: 74].
• $A$ ($0.68\text{V}$) has the lowest reducing power[cite: 74].
The correct decreasing order of reducing power is $B \gt C \gt A$[cite: 74].