Which of the following statements is incorrect?

Options

A. The stability constant of `[Co(NH_(3))_(6)]^(3+)` is greater that of `[Co(NH_(3))_(6)]^(2+)`
B. The cyano complexes are far more stable than those formed by halide ions
C. The stability of halide complexes follows the order `I^(-) lt Br^(-) lt Cl^(-)`
D. The stability constant of `[Cu(NH_(3))_(4)]^(2+)` is greater than that of `[Cu(en)_(2)]^(2+)`

Answer

To determine which statement is incorrect, let’s analyze each statement step by step:

### Step 1: Analyze the first statement
**Statement:** The stability constant of [Co(H2O)6]3+ is greater than [Co(H2O)6]2+.

**Analysis:** The stability of coordination complexes generally increases with the oxidation state of the central metal ion. Since Co(III) has a higher oxidation state than Co(II), [Co(H2O)6]3+ is indeed more stable than [Co(H2O)6]2+.

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

### Step 2: Analyze the second statement
**Statement:** The cyanide complexes are far more stable than those formed by the halides.

**Analysis:** Cyanide (CN-) is a strong field ligand, while halides (like Cl-, Br-, I-) are considered weak field ligands. Strong field ligands tend to form more stable complexes compared to weak field ligands.

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

### Step 3: Analyze the third statement
**Statement:** The stability of halide complexes follows the order I- > Br- > Cl-.

**Analysis:** The stability of halide complexes indeed follows the order I- > Br- > Cl- due to the increasing size and decreasing charge density of the halide ions, which affects their ability to stabilize the metal center.

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

### Step 4: Analyze the fourth statement
**Statement:** The stability constant of [Cu(NH3)4]2+ is greater than that of [Cu(en)2]2+.

**Analysis:** In this case, both complexes have the same oxidation state for copper (+2), but the ligands differ. Ethylenediamine (en) is a bidentate ligand and is a stronger field ligand compared to ammonia (NH3), which is a monodentate ligand. Therefore, [Cu(en)2]2+ should be more stable than [Cu(NH3)4]2+.

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

### Final Conclusion
The incorrect statement is: **The stability constant of [Cu(NH3)4]2+ is greater than that of [Cu(en)2]2+.**

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