What is the formula of aluminium sulphate? 

Al₂(SO₄)₃

The correct answer is option 2. Al₂(SO₄)₃.

The formula of aluminum sulphate is \( Al_2(SO_4)_3 \). Aluminum sulphate, also known as aluminium sulphate, is a chemical compound with the formula \( Al_2(SO_4)_3 \). It consists of two aluminum atoms (\( Al \)) bonded to three sulfate ions (\( SO_4^{2-} \)). This compound is commonly used in water treatment, paper manufacturing, and various industrial processes.