Which of the following statement about `AICI_3` is not correct ?

Options

A. It exists as a dimer
B. It is a covalent compound
C. It involves back bonding between Cl and Al
D. Its aqueous solution conducts electricity

Answer

To determine which statement about AlCl3 is not correct, we will analyze each statement provided:

1. **AlCl3 exists as a dimer.**
- AlCl3 in its anhydrous form exists as a dimer, specifically as Al2Cl6. This means that two AlCl3 molecules combine to form a dimer. This statement is **correct**.

2. **AlCl3 is a covalent compound.**
- AlCl3 is indeed a covalent compound. The bond between aluminum and chlorine is primarily covalent in nature. This statement is **correct**.

3. **AlCl3 involves back bonding between chlorine and aluminum.**
- Back bonding typically refers to the donation of electron density from filled p-orbitals of a ligand (like Cl) to empty d-orbitals of a metal (like Al). In the case of AlCl3, the bonding is primarily through coordinate covalent bonds where Cl donates a pair of electrons to Al's empty p-orbital, but there is no significant back bonding as described. Therefore, this statement is **not correct**.

4. **Its aqueous solution conducts electricity.**
- When AlCl3 is dissolved in water, it dissociates into Al^3+ and Cl^- ions, which can carry electric current. Thus, this statement is **correct**.

In conclusion, the statement that is not correct is: **"It involves back bonding between chlorine and aluminum."**

### Step-by-step Solution:
1. **Identify the statements about AlCl3.**
2. **Analyze the first statement regarding dimer existence.**
- Confirm that AlCl3 exists as a dimer (Al2Cl6) in its anhydrous form.
3. **Analyze the second statement regarding covalent nature.**
- Confirm that AlCl3 is a covalent compound due to the nature of the bonding.
4. **Analyze the third statement regarding back bonding.**
- Determine that there is no significant back bonding in AlCl3; instead, coordinate bonding occurs.
5. **Analyze the fourth statement regarding conductivity in aqueous solution.**
- Confirm that AlCl3 dissociates in water, allowing it to conduct electricity.
6. **Identify the incorrect statement.**
- Conclude that the incorrect statement is about back bonding.