For the net charge to be +3,the mystery charge should beis -2 and net force is towards left.
In first problem, overall charge should be -2 (as mentioned in question).
So charge labelled with ? should be negative charge ( -ve).
There will be net force on -1 charge towards +3 charge (left). For box (b)net force towards right
For box c) net force towards right.
It is often referred to as electric charge, electrical charge, or electrostatic charge, and denoted by the letter q, is a property of a unit of matter that indicates how many more or less electrons than protons it has.
When retained in an electric or magnetic field, matter's basic physical feature known as electric charge causes it to experience a force.
