In which of the following compounds octet is complete and incomplete for all atoms :

Options

A. `{:(Al_(2)Cl_(6),Al_(2)(CH_(3))_(6),AlF_(3),"Dimer of "BeCl_(2),"Dimer of "BeH_(2)),(IC,IC,IC,C,C):}`
B. `{:(Al_(2)Cl_(6),Al_(2)(CH_(3))_(6),AlF_(3),"Dimer of "BeCl_(2),"Dimer of "BeH_(2)),(C,IC,IC,C,IC):}`
C. `{:(Al_(2)Cl_(6),Al_(2)(CH_(3))_(6),AlF_(3),"Dimer of "BeCl_(2),"Dimer of "BeH_(2)),(C,IC,C,IC,IC):}`
D. `{:(Al_(2)Cl_(6),Al_(2)(CH_(3))_(6),AlF_(3),"Dimer of "BeCl_(2),"Dimer of "BeH_(2)),(IC,C,IC,IC,IC):}`

Explanation

To determine whether the octet is complete or incomplete for all atoms in the given compounds, we will analyze each compound step by step.

### Step 1: Analyze Al2Cl6
- **Structure**: Al2Cl6 is a dimer of AlCl3.
- **Chlorine (Cl)**: Each chlorine atom has 7 valence electrons. In Al2Cl6, each Cl atom shares one electron with Al, completing its octet (7 + 1 = 8).
- **Aluminum (Al)**: Aluminum has 3 valence electrons. In Al2Cl6, each Al atom shares electrons with 3 Cl atoms and also receives 2 electrons from the bridged Cl atoms, leading to a total of 6 electrons from the bonds and 2 from the dative bond (3 + 6 = 9). However, since it can expand its octet, it effectively achieves a stable configuration.
- **Conclusion**: All atoms (4 Cl and 2 Al) have complete octets.

### Step 2: Analyze Al2CH6
- **Structure**: Al2CH6 involves aluminum and carbon.
- **Carbon (C)**: Carbon has 4 valence electrons and forms bonds with aluminum. However, it does not have lone pairs to donate.
- **Aluminum (Al)**: Each Al atom shares electrons with carbon, forming three-centered two-electron bonds. Each bond involves 2 electrons (1 from Al and 1 from C), leading to a total of 4 electrons for each Al atom (incomplete octet).
- **Conclusion**: Not all atoms have complete octets.

### Step 3: Analyze AlF3
- **Structure**: AlF3 is an ionic compound.
- **Fluorine (F)**: Each F atom has 7 valence electrons and gains 1 electron from Al, completing its octet (7 + 1 = 8).
- **Aluminum (Al)**: Al loses 3 electrons, resulting in Al^3+ which has the electron configuration of neon (10 electrons).
- **Conclusion**: All atoms (3 F and 1 Al) have complete octets.

### Step 4: Analyze BeCl2
- **Structure**: BeCl2 exists as a dimer.
- **Chlorine (Cl)**: Each Cl atom shares electrons with Be, completing its octet.
- **Beryllium (Be)**: Be has 4 valence electrons and shares 2 electrons with 2 Cl atoms. It also receives 2 electrons from bridged Cl atoms, totaling 6 electrons (incomplete octet).
- **Conclusion**: Not all atoms have complete octets.

### Step 5: Analyze BeH2
- **Structure**: BeH2 also involves bridged hydrogens.
- **Hydrogen (H)**: Each H atom has 1 valence electron and shares it with Be.
- **Beryllium (Be)**: Similar to BeCl2, Be shares electrons with H, leading to a total of 6 electrons (incomplete octet).
- **Conclusion**: Not all atoms have complete octets.

### Final Conclusion:
- **Complete Octet**: Al2Cl6, AlF3
- **Incomplete Octet**: Al2CH6, BeCl2, BeH2

### Summary:
- **Complete for all atoms**: Al2Cl6, AlF3
- **Incomplete for all atoms**: Al2CH6, BeCl2, BeH2