The molecule in which an atom is associated with more than 8 electrons is known as hypervalent molecule and less than 8 electrons is known as hypovalent molecule. All hypervalent molecules must have `ppi-dpi` bonding but the molecules having back bonding back boding need not to have always `ppi-dpi` bondin.
Q. Which of the following is having complete octet:

Options

A. `BeCl_(2)` (dimer)
B. `BeH_(2)` (dimer)
C. `BeH_(2) ` (s)
D. `BeCl_(2)` (s)

Answer

To determine which of the given molecules has a complete octet, we will analyze each molecule step by step.

### Step 1: Understand the Concept of Octet
An octet is achieved when an atom has eight electrons in its valence shell. Atoms tend to gain, lose, or share electrons to achieve a stable octet configuration.

### Step 2: Analyze BeCl2
- **Structure**: Beryllium (Be) has 4 electrons in its valence shell (1s² 2s²). In BeCl2, beryllium forms two bonds with chlorine atoms.
- **Dimer Formation**: BeCl2 exists in a dimeric form as Be2Cl4. Each beryllium atom is bonded to two chlorine atoms.
- **Electron Count**: Each chlorine atom contributes one electron to the bond. Thus, for one beryllium atom:
- 2 electrons from 2 chlorine atoms = 2 (from Cl) + 2 (from Be) = 4 electrons.
- **Conclusion**: Beryllium does not achieve a complete octet in BeCl2.

### Step 3: Analyze BeH2
- **Structure**: Similar to BeCl2, BeH2 has beryllium bonded to two hydrogen atoms.
- **Electron Count**: Each hydrogen contributes one electron:
- 2 electrons from 2 hydrogen atoms = 2 (from H) + 2 (from Be) = 4 electrons.
- **Conclusion**: Beryllium does not achieve a complete octet in BeH2.

### Step 4: Analyze Other Molecules (if provided)
- If there are other molecules in the question, repeat the same analysis as above for each molecule to determine if they achieve a complete octet.

### Step 5: Final Conclusion
After analyzing BeCl2 and BeH2, we conclude that neither achieves a complete octet. If there are other options provided in the question, we would need to analyze those as well to determine which one achieves a complete octet.