Which of the following statement is incorrect regarding `Fe^(2+) and Fe^(3+)` cations?

Options

A. `Fe^(3+)` gives brown colour solution with potassium ferricyanide
B. `Fe^(2+)` gives blue precipitate with potassium ferricyanide
C. `Fe^(3+)` gives red colour solution with potassium thiocyanate
D. `Fe^(2+)` gives brown colour with ammonium thiocyanate

Explanation

To determine which statement is incorrect regarding the cations Fe^(2+) and Fe^(3+), we will analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement 1**: Fe^(3+) gives a brown color solution with potassium ferricyanide.

- When Fe^(3+) reacts with potassium ferricyanide (K₃[Fe(CN)₆]), it forms a complex known as ferric ferricyanide (Fe₃[Fe(CN)₆]₂), which is indeed brown in color.
- **Conclusion**: This statement is correct.

### Step 2: Analyze the Second Statement
**Statement 2**: When Fe^(2+) reacts with potassium ferricyanide, it leads to the formation of a blue precipitate.

- When Fe^(2+) reacts with potassium ferricyanide, it forms a complex called Turnbull's blue (Fe₃[Fe(CN)₆]₂), which precipitates as a blue solid.
- **Conclusion**: This statement is also correct.

### Step 3: Analyze the Third Statement
**Statement 3**: Fe^(3+) gives a red color solution with potassium thiocyanide.

- When Fe^(3+) reacts with potassium thiocyanide (KSCN), it forms a complex ion [Fe(SCN)]^(2+), which is red in color.
- **Conclusion**: This statement is correct as well.

### Step 4: Analyze the Fourth Statement
**Statement 4**: No reaction takes place between Fe^(2+) and ammonium thiocyanate.

- Ammonium thiocyanate (NH₄SCN) does not react with Fe^(2+) to form any complex or color change. Therefore, this statement is incorrect.
- **Conclusion**: This statement is incorrect.

### Final Conclusion
Since statements 1, 2, and 3 are correct, the incorrect statement is statement 4. Thus, the answer to the question is that the fourth statement is incorrect.