Which of the following is a pair of like terms?

1. ab, xy

2. 2xz², -7x²z

3. 4a²b², -$\dfrac{1}{3}$a²bc

4. 0.9 xy, - $\dfrac{2}{11}$ xy

Like terms must have the exact same variables raised to the exact same powers.

Only option 4 has the same variable part (xy) in both terms.

Hence, option 4 is the correct option.