Do you really know all about Coulomb's Force of attraction??

BASIC PRE-REQUISITE KNOWLEDGE-

-All basic knowledge about Coulomb's law.

Now let's discuss about a situation where a particular misconception about Coulomb's law arises.

Let there be two charges Q1 and Q2 in a medium of di-electric constant 'K' and at a distance of 'r'. So, diagramatically, the situation is this- 

Now, I would like to ask 2 questions-

1) What is the Coloumbic force of attraction?

2) Find the net force on a charge particle?

(Now, I am writing the equations and rest of the explanation of this question on the pdf pasted below-)