To determine the correctness of the statements regarding complex ions, we will analyze each statement step by step.
### Step 1: Analyze Statement (A)
**Statement (A): Greater the stability constant of a complex ion, greater is its stability.**
- The stability constant (K) of a complex ion is a measure of the stability of the complex. A higher stability constant indicates that the formation of the complex is favored and that the complex is less likely to dissociate back into its components (metal ion and ligands).
- Therefore, this statement is **correct**.
### Step 2: Analyze Statement (B)
**Statement (B): Greater the oxidation state of the central metal ion, greater is the stability of the complex.**
- Generally, as the oxidation state of the central metal ion increases, the positive charge on the metal ion increases. This leads to a stronger electrostatic attraction between the metal ion and the ligands, which can enhance the stability of the complex.
- Therefore, this statement is also **correct**.
### Step 3: Analyze Statement (C)
**Statement (C): CO stabilizes complex because of its synergic bonding.**
- Carbon monoxide (CO) can form strong complexes with metal ions due to synergic bonding. In this type of bonding, there is both σ (sigma) donation from the lone pair of electrons on the carbon atom to the metal and π (pi) back-donation from the filled d-orbitals of the metal to the empty π* orbitals of CO.
- This dual interaction enhances the stability of the complex.
- Therefore, this statement is **correct**.
### Step 4: Analyze Statement (D)
**Statement (D): Chelate complexes have low stability constants.**
- Chelate complexes, which are formed by ligands that can bind to a metal ion at multiple sites (forming a ring structure), are generally more stable than non-chelating complexes. This is due to the "chelate effect," which results in a significant increase in stability.
- Therefore, this statement is **incorrect**.
### Conclusion
- Statements (A), (B), and (C) are correct.
- Statement (D) is incorrect.
Thus, the number of correct statements is **3** (A, B, C).
### Final Answer:
**The number of correct statements is 3.**
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