Which of the following cannot give iodometric titrations?

Options

A. `Ag^+`
B. `Fe^(3+)`
C. `Pb^(2+)`
D. `Cu^(2+)`

Answer

To solve the question "Which of the following cannot give iodometric titrations?" we need to analyze the options provided: Ag⁺, Fe³⁺, Pb²⁺, and Cu²⁺.

### Step-by-Step Solution:

1. **Understanding Iodometric Titration**:
Iodometric titration involves the oxidation of iodide ions (I⁻) to iodine (I₂) by a substance in a higher oxidation state. The liberated iodine can then be titrated with a reducing agent, typically sodium thiosulfate (Na₂S₂O₃).

**Hint**: Remember that iodometric titrations require a species that can oxidize iodide ions to iodine.

2. **Analyzing Each Ion**:
- **Ag⁺ (Silver Ion)**: Silver in the +1 oxidation state can oxidize iodide ions to iodine.
- **Fe³⁺ (Iron Ion)**: Iron in the +3 oxidation state can also oxidize iodide ions to iodine.
- **Cu²⁺ (Copper Ion)**: Copper in the +2 oxidation state can oxidize iodide ions to iodine.
- **Pb²⁺ (Lead Ion)**: Lead in the +2 oxidation state is in a lower oxidation state compared to the others and cannot oxidize iodide ions to iodine.

**Hint**: Compare the oxidation states of each ion and determine their ability to oxidize iodide ions.

3. **Conclusion**:
Since Pb²⁺ is in the lowest oxidation state among the given ions, it cannot oxidize iodide ions to iodine. Therefore, it cannot participate in iodometric titrations.

**Final Answer**: The ion that cannot give iodometric titrations is **Pb²⁺** (Lead Ion).

### Summary:
The correct option is **C: Pb²⁺**.