Number of the following statements is/are correct?
(A) Greater the stability constant of a complex ion, greater is its stability
(B) Greater the oxidation state of the central metal ion, greater is the stability of the complex
(C ) CO stabilises complex becuase of its synergic Bonding.
(D) Chelate complexes have low stability constants

Answer

To solve the question regarding the correctness of the statements about complex ions, let's analyze each statement one by one.

### Step 1: Analyze Statement A
**Statement A:** Greater the stability constant of a complex ion, greater is its stability.

**Explanation:** The stability constant (K) of a complex ion is a measure of the stability of the complex. A higher stability constant indicates that the complex is more stable because it implies that the equilibrium lies more to the right, favoring the formation of the complex over its dissociation into the metal ion and ligands.

**Conclusion:** 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.

**Explanation:** Generally, a higher oxidation state of the central metal ion can lead to increased stability of the complex due to stronger electrostatic interactions between the metal ion and the ligands. However, this is not universally true for all ligands and complexes. The stability can also depend on the nature of the ligands and the specific metal involved. For example, some ligands may stabilize lower oxidation states better.

**Conclusion:** This statement is **partially correct**, but it is not universally applicable.

### Step 3: Analyze Statement C
**Statement C:** CO stabilizes complex because of its synergic bonding.

**Explanation:** Carbon monoxide (CO) is indeed a strong field ligand that stabilizes metal complexes through synergic bonding. In this process, CO forms a sigma bond with the metal and can also engage in back-donation, where electrons from the filled d-orbitals of the metal are donated to the empty π* orbitals of CO. This dual interaction enhances the stability of the complex.

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

### Step 4: Analyze Statement D
**Statement D:** Chelate complexes have low stability constants.

**Explanation:** Chelate complexes are formed when a ligand binds to a metal ion at multiple points, creating a ring structure. This ring formation significantly increases the stability of the complex due to the chelate effect. Therefore, chelate complexes typically have high stability constants, not low.

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

### Final Conclusion
Now, let's summarize the correctness of each statement:
- Statement A: Correct
- Statement B: Partially correct (but generally considered correct in many contexts)
- Statement C: Correct
- Statement D: Incorrect

Thus, the number of correct statements is **3** (A, C, and B considered correct in many contexts).