Question

how does the force between two pt charges change if the dielectric constant of the medium increases

Answer 1

Dielectric constant (K) of a medium is defined as the ratio of forces of attraction/ repulsion between two point charges separated by a certain distance in air/ vacuum to the force of attraction / repulsion between the same two point charges, held the same distance apart in the medium.
i.e., F_m​ = F₀/K.
so, with increasing dielectric constant of the medium, the force between two point charges decreases.