To identify the set with the stronger interaction between the charged objects, the most relevant question the student can ask is:
Are the objects both positively charged or both negatively charged?
This is because the nature of the charges (whether they are both positive, both negative, or one of each) directly affects the interaction. Like charges repel and opposite charges attract. If both objects in a set are either positive or negative, they will repel each other, while one positive and one negative will attract. The magnitude of the charges (both being ±1 Coulomb) is the same, but the type of interaction (attractive or repulsive) will influence the strength of the overall interaction.
The other options (distance, size, and mass) do not directly determine the nature and strength of the electric interaction in the way the charge types do.