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 can follow these steps:

### Step-by-Step Solution:

1. **Identify the Type of Complex**:
The complex \( MA_3B_3 \) is an octahedral complex because it has a coordination number of 6 (3 ligands of type A and 3 ligands of type B).

**Hint**: Remember that octahedral complexes have a coordination number of 6.

2. **Determine the Possible Geometrical Isomers**:
In octahedral complexes with two different types of ligands, we can have two types of geometrical isomers:
- **Facial (fac)**: where the same type of ligands occupy adjacent positions.
- **Meridional (mer)**: where the same type of ligands occupy positions that are opposite each other.

**Hint**: Visualize the arrangement of ligands in octahedral geometry to distinguish between facial and meridional isomers.

3. **Draw the Geometrical Isomers**:
- For the **fac** isomer, the three A ligands will be on one face of the octahedron, and the three B ligands will be on the opposite face.
- For the **mer** isomer, the three A ligands will occupy one plane of the octahedron, and the three B ligands will be in the opposite plane.

**Hint**: Sketch the octahedron and label the positions of ligands A and B to visualize the arrangements.

4. **Check for Optical Isomers**:
Next, we need to check if these geometrical isomers can exhibit optical isomerism. Optical isomers are non-superimposable mirror images.
- For both the fac and mer isomers, there is a plane of symmetry present. This means that they cannot have optical isomers.

**Hint**: Look for planes of symmetry in your drawings to determine if optical isomers are possible.

5. **Count the Total Number of Stereoisomers**:
Since we have identified 2 geometrical isomers (fac and mer) and no optical isomers, the total number of stereoisomers for the complex \( MA_3B_3 \) is 2.

**Hint**: Sum the number of geometrical isomers and optical isomers to find the total.

### Final Answer:
The number of possible stereoisomers in \( MA_3B_3 \) is **2** (both geometrical isomers: fac and mer).