The standard reduction potential (E°) values of $Ag^+|Ag, K^+|K, Mg^{2+}|Mg$ and $Cr^{3+}|Cr$ are 0.80 V, -2.93 V, -2.37 V and -0.74 V, respectively. The decreasing order of reducing power of the following metals is
(A) Ag
(B) K
(C) Mg
(D) Cr
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B), (C), (D), (A)
The reducing power of a metal is its tendency to lose electrons (get oxidized), i.e., act as a reducing agent.
The standard reduction potential (E°) given is for the half-reaction: Mⁿ⁺ + ne⁻ → M
- A more negative (or lower) E° means the reduction is less favorable → the reverse reaction (oxidation of metal) is more favorable → stronger reducing agent.
- A more positive (or higher) E° means the metal is weaker as a reducing agent.
Given E° values:
- Ag⁺/Ag: +0.80 V
- Cr³⁺/Cr: –0.74 V
- Mg²⁺/Mg: –2.37 V
- K⁺/K: –2.93 V
Decreasing order of reducing power (strongest → weakest): K > Mg > Cr > Ag
Corresponding to options: (B) K > (C) Mg > (D) Cr > (A) Ag
Thus, the correct choice is (B), (C), (D), (A).