All elements except carbon have tendency to show maximum covalency of six

Options

A. Due to absence of vacant d-orbitals
B. Due to presence of vacant d-orbitals
C. Due to presence of partially filled d-orbitals.
D. Due to presence of completely filled d-orbitals.

Answer

To solve the question "All elements except carbon have a tendency to show a maximum covalency of six," we will analyze the electronic configurations of the elements in the carbon family and understand the role of vacant d-orbitals in determining covalency.

### Step-by-Step Solution:

1. **Identify the Elements in the Carbon Family**:
The carbon family consists of carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb).

2. **Covalency of Carbon**:
- Carbon has an electronic configuration of \(1s^2 2s^2 2p^2\).
- The maximum covalency of carbon is 4, which is due to its ability to form four covalent bonds by using its four valence electrons (two from 2s and two from 2p orbitals).
- Importantly, carbon lacks vacant d-orbitals, which limits its ability to expand its covalency beyond 4.

3. **Covalency of Silicon, Germanium, Tin, and Lead**:
- Silicon has an electronic configuration of \(1s^2 2s^2 2p^6 3s^2 3p^2\).
- Germanium has an electronic configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^2\).
- Tin and lead also have similar configurations with filled d-orbitals.
- These elements have vacant d-orbitals available for bonding, which allows them to expand their covalency beyond 4.

4. **Presence of Vacant d-Orbitals**:
- The presence of vacant d-orbitals in silicon, germanium, tin, and lead enables these elements to form more than four bonds.
- They can utilize these d-orbitals to accommodate additional electrons, allowing them to achieve a maximum covalency of 6.

5. **Examples of Compounds**:
- Silicon can form compounds like \(SiF_6^{2-}\).
- Germanium can form \(GeCl_6^{2-}\).
- Lead can form \(PbCl_6^{2-}\).
- These compounds illustrate that the covalency can reach up to 6 due to the involvement of d-orbitals.

6. **Conclusion**:
- The reason that all elements except carbon can show a maximum covalency of 6 is due to the presence of vacant d-orbitals in their electronic configurations, which allows them to expand their bonding capacity.

### Final Answer:
All elements except carbon have a tendency to show a maximum covalency of six due to the presence of vacant d-orbitals, which allows them to form more than four covalent bonds.