Question

Arrange the following redox couples in the increasing order of their reducing strength:
Cu$^{2+}$/Cu$^{+}$ $E^\circ = -0.34$ V
Ag$^+$/Ag $E^\circ = -0.8$ V
Ca$^{2+}$/Ca  $E^\circ = +2.87$ V
Cr$^{3+}$/Cr$^{2+}$  $E^\circ = +0.74$ V

• A. $B<A<D<C$
• B. $A<B<D<C$
• C. $C<A<D<B$
• D. $D<A<B<C$

Hint:

In redox reactions, a more negative $E^\circ$ indicates a stronger reducing agent, while a more positive $E^\circ$ indicates a stronger oxidizing agent.

Answer 1

The Correct Option is A

To arrange the redox couples in the increasing order of their reducing strength, we need to look at the values of their standard electrode potentials ($E^\circ$). The standard electrode potential indicates the ability of a species to gain electrons (reduction potential). A more negative $E^\circ$ value means a weaker tendency to reduce, and hence a stronger tendency to act as a reducing agent. 
- For [A] Cu$^{2+}$/Cu$^{+}$, $E^\circ = -0.34$ V, so this species is a weak reducing agent. 
- For [B] Ag$^+$/Ag, $E^\circ = -0.8$ V, indicating an even weaker reducing agent than [A]. 
- For [D] Cr$^{3+}$/Cr$^{2+}$, $E^\circ = +0.74$ V, indicating a stronger reducing agent than both [A] and [B]. 
- For [C] Ca$^{2+}$/Ca, $E^\circ = +2.87$ V, making this the strongest reducing agent. 
Thus, the order of reducing strength from weakest to strongest is: B<A<D<C