A point charge of 10 bold italic mu C is placed at the cente

A point charge of -10 bold italic mu C is placed at the center of a square.

A point charge or -10 mu c is placed at the center or a square. When a second point charge or -5 mu c is placed at one or the square\'s corners, it is observed that an electrostatic force of 4.0 N acts on the negative charge at the square\'s center. Now, identical charges of -5 mu C are placed at the other three corners of the square. The magnitude of the net electrostatic force acting on the positive charge at the center of the square is N.

Solution

In your question the net force on any charge placed at the center will be zero, irrespective of the magnitude and sign of the test charge. This is because of symmetry of the square or any other symmetric object like polygon or hexagon as long as the charges placed at their corners are equal in sign and magnitude.