The number of possible sterio isomers in `Ma_(3)b_(3)` is equal to
(Here a, b are different monodentate ligands).

Answer

To determine the number of possible stereoisomers for the complex \( MA_3B_3 \), where \( A \) and \( B \) are different monodentate ligands, we will analyze the structure and types of isomers that can arise from this coordination complex.

### Step-by-Step Solution:

1. **Identify the Geometry of the Complex:**
- The complex \( MA_3B_3 \) has an octahedral geometry because it consists of six ligands surrounding a central metal atom \( M \).

2. **Determine the Types of Isomers:**
- In octahedral complexes with two types of ligands, we can have geometrical isomers. The two main types of geometrical isomers are:
- **Facial (fac) Isomers:** where three identical ligands occupy one face of the octahedron.
- **Meridional (mer) Isomers:** where three identical ligands are arranged in such a way that two of them are on one side and the other one is on the opposite side.

3. **Draw the Possible Isomers:**
- **Facial Isomer:** In this arrangement, the three \( A \) ligands are adjacent to each other, forming a face of the octahedron, while the three \( B \) ligands occupy the opposite face.
- **Meridional Isomer:** In this arrangement, two \( A \) ligands are on one side of the octahedron, and the third \( A \) ligand is on the opposite side, with the \( B \) ligands arranged similarly.

4. **Check for Optical Isomers:**
- For optical isomers to exist, the complex must lack a plane of symmetry.
- In both the facial and meridional arrangements, there is a plane of symmetry present. Therefore, neither of these configurations will have optical isomers.

5. **Count the Total Stereoisomers:**
- We have identified two geometrical isomers (fac and mer) and confirmed that there are no optical isomers.
- Thus, the total number of stereoisomers for the complex \( MA_3B_3 \) is **2**.

### Final Answer:
The number of possible stereoisomers in \( MA_3B_3 \) is **2**.

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