In `IF_(6)^(-) and TeF_(5)^(-)`, sum of axial d-orbitals which are used in hybridisation in both species.

Answer

To solve the problem of finding the sum of axial d-orbitals used in hybridization for the species IF6^- and TeF5^-, we can follow these steps:

### Step 1: Determine the Electron Configuration of Iodine and Tellurium
- Iodine (I) is in group 17 and has 7 valence electrons. With the negative charge in IF6^-, it gains an additional electron, giving it a total of 8 valence electrons.
- Tellurium (Te) is in group 16 and has 6 valence electrons. With the negative charge in TeF5^-, it gains an additional electron, giving it a total of 7 valence electrons.

### Step 2: Count the Number of Bond Pairs and Lone Pairs
- In IF6^-, there are 6 fluorine atoms bonded to iodine, resulting in 6 bond pairs. Additionally, there is 1 lone pair on iodine. Therefore, the steric number for IF6^- is 6 (bond pairs) + 1 (lone pair) = 7.
- In TeF5^-, there are 5 fluorine atoms bonded to tellurium, resulting in 5 bond pairs. Additionally, there is 1 lone pair on tellurium. Therefore, the steric number for TeF5^- is 5 (bond pairs) + 1 (lone pair) = 6.

### Step 3: Determine the Hybridization
- For IF6^-, with a steric number of 7, the hybridization is Sp^3d^3.
- For TeF5^-, with a steric number of 6, the hybridization is Sp^3d^2.

### Step 4: Identify the Axial d-Orbitals
- In the case of IF6^-, the hybridization Sp^3d^3 involves the following d-orbitals: dx^2-y^2, dxz, dyz, and dxy. The axial d-orbitals are dxz and dyz, which are oriented along the z-axis.
- In the case of TeF5^-, the hybridization Sp^3d^2 involves the d-orbitals: dx^2-y^2 and dz^2. The axial d-orbitals are dz^2 and dx^2-y^2.

### Step 5: Count the Axial d-Orbitals
- For IF6^-, there are 2 axial d-orbitals (dxz and dyz).
- For TeF5^-, there are also 2 axial d-orbitals (dz^2 and dx^2-y^2).

### Step 6: Calculate the Sum of Axial d-Orbitals
- The total number of axial d-orbitals used in both species is 2 (from IF6^-) + 2 (from TeF5^-) = 4.

### Final Answer
The sum of axial d-orbitals used in hybridization in both IF6^- and TeF5^- is **4**.

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