Double salts are addition compounds which lose their identity in aqueous solution whereas complexes which are also addition compounds do not lose their identity in aqueous solution. The coordination compounds show isomerism and find applications in photography, qualitative analysis, metallurgy, water purification and in the treatment of various diseases .
Which of the following statment is incorrect ?

Options

A. Alum is a double salt
B. EDTA salt of calcium is used in the treatment of lead poisoning.
C. Effective atomic number of the metal in complexes `[Ni(CO)_(4)] and [Fe(CN)_(6)]^(4-)` is same.
D. Chloridotris (triphenylphosphine) rhodium (I) is effective heterogeneous catalyst for hydrogenation of alkenes.

Explanation

To solve the question regarding the incorrect statement about coordination compounds and double salts, we will analyze each statement provided in the options one by one.

### Step-by-Step Solution:

1. **Understanding Double Salts and Complexes**:
- Double salts are compounds that consist of two different salts that crystallize together. They lose their identity in aqueous solution, meaning they dissociate into their constituent ions when dissolved in water.
- Complexes, on the other hand, are coordination compounds that retain their identity in solution. They do not dissociate into individual ions but remain as intact entities.

2. **Analyzing Statement A**:
- **Statement**: "Alum is a double salt."
- **Analysis**: Alum is indeed a double sulfate salt of aluminum, commonly represented as KAl(SO4)2·12H2O. When dissolved in water, it dissociates into its ions (K⁺, Al³⁺, and SO₄²⁻). Therefore, this statement is **correct**.

3. **Analyzing Statement B**:
- **Statement**: "EDTA salt of calcium is used in the treatment of lead poisoning."
- **Analysis**: EDTA (Ethylenediaminetetraacetic acid) forms stable complexes with lead ions (Pb²⁺), effectively chelating them and allowing for their excretion from the body. This statement is also **correct**.

4. **Analyzing Statement C**:
- **Statement**: "The effective atomic number for the metal in complexes Ni(CO)₄ and Fe(CN)₆⁴⁻ is the same."
- **Analysis**:
- For Ni(CO)₄: Nickel (Ni) has an atomic number of 28. CO is a neutral ligand contributing 2 electrons per ligand. Therefore, EAN = 28 (atomic number) + 4*2 (from CO) = 28 + 8 = 36.
- For Fe(CN)₆⁴⁻: Iron (Fe) has an atomic number of 26. In the +2 oxidation state (Fe²⁺), EAN = 26 - 2 + 6*2 (from CN) = 24 + 12 = 36.
- Since both complexes have the same EAN of 36, this statement is **correct**.

5. **Analyzing Statement D**:
- **Statement**: "Chlorotris(triphenylphosphine)rhodium(I) is an effective heterogeneous catalyst for carrying out hydrogenation of alkenes."
- **Analysis**: This complex is known as Wilkinson's catalyst (RhCl(PPh₃)₃), which is indeed used for the hydrogenation of alkenes. Therefore, this statement is also **correct**.

### Conclusion:
After analyzing all the statements, we find that all statements A, B, C, and D are correct. Therefore, there is no incorrect statement among the options provided.

### Final Answer:
All statements are correct; there is no incorrect statement.

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