Electric Charges and Fields

These questions consist of two statements, each printed as assertion and reason. While answering these question you are required to choose any one of the following five responses.
Consider two positive charges, each of magnitude $$q$$, placed on the y-axis at the point $$(0, a)$$ and $$(0, -1)$$. A positively charged particle of change $$q'$$ and mass $$m$$ is displaced slightly from the origin in the direction of the positive x-axis.
Two equal balls having equal positive charge $$'q'$$ coulombs are suspended by two insulating strings of equal length. What would be the effect on the force when a plastic sheet is inserted between the two?
Force of interaction between two co-axis short electric dipoles whose centres are $$R$$ distance apart varies as
Two point charges $$+q$$ and $$+q$$ are fixed at $$ (a,0,0)$$ and $$ (-a,0,0)$$. A third point charge $$-q$$ is at origin.