Which of the following statements about aluminium chloride is incorrect?

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

Explanation

To determine which statement about aluminum chloride (AlCl3) is incorrect, let's analyze each statement step by step.

### Step 1: Analyze the first statement
**Statement:** Aluminum chloride exists as a dimer.

**Explanation:** In its anhydrous form, AlCl3 exists as a dimer (Al2Cl6). This means that two AlCl3 units combine to form a larger molecule. This statement is correct.

### Step 2: Analyze the second statement
**Statement:** Aluminum chloride is a covalent compound.

**Explanation:** AlCl3 is indeed a covalent compound, especially in its anhydrous form. The bonding between aluminum and chlorine involves sharing of electrons, which is characteristic of covalent compounds. This statement is also correct.

### Step 3: Analyze the third statement
**Statement:** Aluminum chloride conducts electricity only in its hydrated form.

**Explanation:** When AlCl3 is hydrated, it dissociates into ions (Al^3+ and Cl^-) in solution, allowing it to conduct electricity. However, in its anhydrous form, it does not conduct electricity because it does not have free ions. This statement is correct.

### Step 4: Analyze the fourth statement
**Statement:** Aluminum chloride involves backbonding between chlorine and aluminum.

**Explanation:** This statement is incorrect. Aluminum chloride (AlCl3) is an electron-deficient molecule, meaning it does not have enough electrons to complete its octet. Instead of backbonding, the bonding between aluminum and chlorine is primarily through coordinate bonds, where chlorine donates a pair of electrons to aluminum. Therefore, this statement is incorrect.

### Conclusion
The incorrect statement about aluminum chloride is the one that claims it involves backbonding between chlorine and aluminum.

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