If you have two charges q1 and q2, you can get the force between them F by multiplying them with the coulomb constant K (approximately 9 × 10^9) and then dividing that by the distance between them squared r^2.
q1 and q2 cannot be negative. Sometimes you’ll not be given a charge, and instead the problem will tell you that you have a proton or electron, both of them have the same charge (1.6 × 10^-19 C), but electrons have a negative charge.
q1 and q2 can be negative. The force is the same as if they were positive because -1 x -1 = 1
But that if both are negative not one pos one neg like the previous commenter gave in their examples, so the true formula has an absolute value in the numerator: |q1Xq2|
In this case yes, but if q1 was -20μC, q2 was 30μC, and r was 0.5m, then using -20μC as it is would make F equal to -21.6N which is just 21.6N of attraction force between the two charges.
If they are oppositely charged particles, I would expect that there is a force of attraction acting on them, yes.
