Two particles A and B having charges q and 2q respectively are placed on a smooth horizontal table with a separation d. A third particle C is to be clamped on the table in such a way that the particles A and B remain at rest under the electrical forces. What shud be the charge on C????

ne1

A charge Q of magnitude -2q(3-2)  must be kept in between q and 2q at a distance of d( - 1) from charge q.

This question was asked previously by somebody.I solved it there.Anyway,Harsha is right.

Do we have to consider the equilibrium of the charge placed in btween them also????