Which of the following statement is/are not true ?

Options

A. `Fe_((aq))^(2+)` gives brown colour with `NH_(4)SCN`
B. `Fe_((aq))^(3+)` gives blood red colour with `NH_(4)SCN`
C. `Fe_((aq))^(2+)`yieids colour with `K_(2)Fe(CN)_(6)`
D. `Ag^(o+)`reacts with `CO_(3)^(2-)` then black ppt is formed

Answer

To determine which of the statements provided are not true, we will analyze each statement one by one based on qualitative inorganic salt analysis principles.

### Step-by-Step Solution:

1. **Statement 1: Fe²⁺ gives brown color with ammonium thiocyanide.**
- When Fe²⁺ ions react with ammonium thiocyanide (NH₄SCN), they form a complex known as hexathiocyanate ferrate(II), which is brown in color.
- **Conclusion:** This statement is **true**.

2. **Statement 2: Fe³⁺ gives blood red color with ammonium thiocyanate.**
- When Fe³⁺ ions react with ammonium thiocyanate, they form a complex that is blood red in color, known as the thiocyanatoiron(III) complex.
- **Conclusion:** This statement is **true**.

3. **Statement 3: Fe²⁺ yields blue color with K₂[Fe(CN)₆].**
- When Fe²⁺ ions react with potassium ferrocyanide (K₂[Fe(CN)₆]), they form a blue precipitate known as Turnbull's blue (ferrous ferrocyanide).
- **Conclusion:** This statement is **true**.

4. **Statement 4: Ag⁺ reacts with CO₃²⁻ to form a black precipitate.**
- When Ag⁺ ions react with carbonate ions (CO₃²⁻), they form silver carbonate (Ag₂CO₃), which is a pale yellow precipitate, not black.
- **Conclusion:** This statement is **not true**.

### Final Answer:
The statement that is not true is **Statement 4**: "Ag⁺ reacts with CO₃²⁻ to form a black precipitate."

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