Answer:
It is 1.
Step-by-step explanation:
Assuming no other forces present, the electrostatic force obeys the Coulomb's law, which can be expressed as follows:
At the same time, it obeys the Newton's 3rd law, which implies that regardless of the values of the charges and the distance between them, the force exerted on both charges must be the same in magnitude and opposite each other.
So, the ratio of the electrostatic force on X to that on Y is just 1, as both forces are equal each other.