Which of the following is/are correct for potassium ferrocyanide ?

Options

A. It gives a brown precipitate with `Cu^(2+)` ions.
B. It gives a white precipitate of mixed salt with `Ca^(2+)` ions.
C. It in excess gives a bluish white/white precipitate with `Zn^(2+)`
D. It develops a deep red colouration with `Fe^(3+)`

Answer

To determine which statements are correct regarding potassium ferrocyanide (K₄[Fe(CN)₆]), we will analyze each option step by step.

### Step 1: Understanding Potassium Ferrocyanide
Potassium ferrocyanide is a coordination compound with the formula K₄[Fe(CN)₆]. It contains the ferrocyanide ion [Fe(CN)₆]⁴⁻, where iron is in the +2 oxidation state.

### Step 2: Analyzing the Options

1. **Option A: It gives a brown precipitate with Cu²⁺.**
- When potassium ferrocyanide reacts with copper(II) ions (Cu²⁺), it forms a complex that results in a reddish-brown precipitate, specifically Cu₂[Fe(CN)₆]. Therefore, this statement is correct.

2. **Option B: It gives a white precipitate with Ca²⁺.**
- When potassium ferrocyanide reacts with calcium ions (Ca²⁺), it forms a white precipitate of Ca(NH₄)K[Fe(CN)₆]. Thus, this statement is also correct.

3. **Option C: It gives a bluish-white precipitate with Zn²⁺ in excess.**
- When potassium ferrocyanide reacts with zinc ions (Zn²⁺), it forms Zn₂[Fe(CN)₆], which is indeed a white precipitate. Therefore, this statement is correct as well.

4. **Option D: It develops a deep red coloration with Fe³⁺.**
- When potassium ferrocyanide reacts with ferric ions (Fe³⁺), it forms a complex known as Prussian blue, which is not deep red but rather blue in color. Therefore, this statement is incorrect.

### Conclusion
The correct options for potassium ferrocyanide are:
- Option A: Correct
- Option B: Correct
- Option C: Correct
- Option D: Incorrect

Thus, the correct statements are A, B, and C.

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