Which of the following statements is incorrect ?

Options

A. In equilibrium mixture of ice and water kept in perfectly insulated flask mass of ice and water does not change with time.
B. The intensity of red colour increases when oxalic acid is added to a solution containing iron (III) nitrate and potassium thiocyanate.
C. On addition of catalyst the equilibrium constant value is not affected.
D. Equilibrium constant for a reaction with negative `DeltaH` value decreases as the temperature increases.

Explanation

To solve the question regarding which statement is incorrect, we will analyze each option step by step.

### Step 1: Analyze the first statement
**Statement:** In an equilibrium mixture of ice and water, kept in a perfectly insulated flask, the mass of ice and water does not change with time.

**Analysis:**
- In an equilibrium state, the processes of ice melting into water and water freezing back into ice occur at equal rates.
- Since the flask is perfectly insulated, there is no heat exchange with the surroundings, and thus the temperature remains constant.
- Therefore, the mass of ice and water will remain constant over time.

**Conclusion:** This statement is **correct**.

### Step 2: Analyze the second statement
**Statement:** The intensity of red color increases when oxalic acid is added to a solution containing iron(III) nitrate and potassium thiocyanate.

**Analysis:**
- The reaction between iron(III) ions (Fe³⁺) and thiocyanate ions (SCN⁻) produces a red complex (Fe(SCN)²⁺).
- Adding oxalic acid will react with Fe³⁺ ions, reducing their concentration.
- According to Le Chatelier's principle, if the concentration of a reactant decreases, the equilibrium will shift to the left, resulting in a decrease in the concentration of the red complex.
- Consequently, the intensity of the red color will decrease, not increase.

**Conclusion:** This statement is **incorrect**.

### Step 3: Analyze the third statement
**Statement:** On addition of a catalyst, the equilibrium constant value is not affected.

**Analysis:**
- A catalyst speeds up the rate of both the forward and reverse reactions equally, allowing the system to reach equilibrium faster.
- However, it does not change the position of equilibrium or the equilibrium constant.

**Conclusion:** This statement is **correct**.

### Step 4: Analyze the fourth statement
**Statement:** The equilibrium constant for a reaction with a negative ΔH value decreases as the temperature increases.

**Analysis:**
- For exothermic reactions (negative ΔH), increasing the temperature shifts the equilibrium to the left (toward the reactants) according to Le Chatelier's principle.
- As a result, the concentration of products decreases, leading to a decrease in the equilibrium constant.

**Conclusion:** This statement is **correct**.

### Final Conclusion
After analyzing all the statements:
- The first statement is correct.
- The second statement is incorrect.
- The third statement is correct.
- The fourth statement is correct.

Thus, the answer to the question is that **the second statement is incorrect**.

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