The reduction potentials of `Zn, Cu, Fe` and `Ag` are in the increasing order:

Options

A. `Zn, Cu, Fe, Ag`
B. `Cu, Ag, Fe, Zn`
C. `Ag, Cu, Fe, Zn`
D. `Fe, Zn, Cu, Ag`

Answer

To determine the increasing order of reduction potentials for the metals zinc (Zn), copper (Cu), iron (Fe), and silver (Ag), we can follow these steps:

### Step 1: Understand Reduction Potentials
Reduction potential (E°) indicates how easily a metal ion can gain electrons to become a neutral metal. A higher (more positive) reduction potential means the metal is more likely to be reduced, while a lower (more negative) reduction potential indicates a lesser tendency to gain electrons.

### Step 2: Refer to the Reactivity Series
The reactivity series of metals helps us understand their relative reactivity and reduction potentials. In general, metals that are more reactive have lower (more negative) reduction potentials.

### Step 3: Position the Metals in the Reactivity Series
- **Zinc (Zn)**: More reactive than iron and copper; it has a negative reduction potential.
- **Iron (Fe)**: Less reactive than zinc but more reactive than copper and silver; it has a negative reduction potential but is higher than zinc.
- **Copper (Cu)**: Less reactive than iron and zinc; it has a positive reduction potential.
- **Silver (Ag)**: Least reactive among the four; it has the highest (most positive) reduction potential.

### Step 4: List the Metals in Order of Increasing Reduction Potential
Based on the above analysis, we can arrange the metals in order of increasing reduction potential:
1. Zinc (Zn) - lowest reduction potential
2. Iron (Fe) - higher than zinc
3. Copper (Cu) - higher than iron
4. Silver (Ag) - highest reduction potential

### Final Order
Thus, the increasing order of reduction potentials for Zn, Cu, Fe, and Ag is:
**Zn < Fe < Cu < Ag**