Iodimetric titrations are usually performed in neutral or mildly alkaline (pH = 8) or weakly acidic solutions. Which statement is not valid for this observation ?

Options

A. In strong alkaline solution, `I_2` disproportionate to `I^(-) and IO^(-)`
B. In strong acidic solutions , starch used to detect the end point tends to hydrolyse or decompose
C. `I^-` produced during titration tends to be oxidized by dissolved oxygen in acidic medium
D. Reducing power of reducing agent is increased in strong acidic medium

Answer

To solve the question regarding iodimetric titrations and identify which statement is not valid, we will analyze the provided options step by step.

### Step 1: Understand the context of iodimetric titrations
Iodimetric titrations involve the use of iodine (I2) as a titrant. The pH of the solution is crucial because it affects the behavior of iodine and the reactions involved.

**Hint:** Recall that the pH of a solution can influence the stability of iodine and its interaction with other species.

### Step 2: Analyze the statements
We need to evaluate each statement provided in the options to determine which one is incorrect regarding the behavior of iodine in different pH conditions.

1. **Statement 1:** In a strong alkaline solution, I2 disproportionates to I- and IO-.
- This statement is valid. In a strong alkaline environment, iodine can disproportionate into iodide ions (I-) and hypoiodite ions (IO-).

2. **Statement 2:** In a strong acidic solution, starch used to detect the endpoint tends to hydrolyze or decompose.
- This statement is also valid. Starch can hydrolyze in acidic conditions, which would affect its ability to indicate the endpoint of the titration.

3. **Statement 3:** I- produced during titration tends to oxidize by dissolved oxygen in acidic medium.
- This statement is valid. Iodide ions (I-) can be oxidized back to iodine (I2) in the presence of dissolved oxygen, particularly in acidic conditions.

4. **Statement 4:** Reducing power of a reducing agent is increased in a strong acidic medium.
- This statement is **not valid**. In a strong acidic medium, the reducing power of I- does not increase; instead, it can decrease as the reaction may reverse, converting I- back to I2.

### Step 3: Conclusion
The statement that is not valid for the observation regarding iodimetric titrations is **Statement 4**. Thus, the correct answer is option 4.

**Final Answer:** Option 4 is not valid.