Commutative Law of Binary Operation

Q. Let * be the binary operation defined on Q. Which of the following binary operations are commutative?

1. a * b = a – b ∀ a, b ∈ Q
2. a * b = $a^2+b^2$ ∀ a, b ∈ Q
3. a * b = a + ab ∀ a, b ∈ Q
4. a * b =$(a–b{)}^2$ ∀ a, b ∈ Q