**Electric Force Between Two Point Charges**

The electric force between two point charges q and Q at rest can be calculated using Coulomb's Law:

F = k * (q * Q) / r^2

where F is the magnitude of the electric force, k is the electrostatic constant (k = 8.99 × 10^9 N m^2/C^2), q and Q are the magnitudes of the charges, and r is the distance between them.

**Total Force on Q**

Now, let's consider the scenario where a charge -q is placed next to the charge q. We want to determine the total force on the charge Q. To find the net force, we need to consider the individual forces between each charge and Q.

1. **Force between Q and q:**
The force between Q and q is given by Coulomb's Law as F1 = k * (q * Q) / r1^2, where r1 is the distance between Q and q.

2. **Force between Q and -q:**
Similarly, the force between Q and -q is given by Coulomb's Law as F2 = k * (q * -q) / r2^2, where r2 is the distance between Q and -q.

3. **Calculating the total force:**
The total force on Q is the vector sum of the individual forces. Since the charges q and -q are placed next to each other, their forces on Q will have opposite directions. Thus, we need to consider the magnitudes and directions of F1 and F2.

- If q and -q are equidistant from Q, i.e., r1 = r2:
In this case, the magnitudes of F1 and F2 will be the same, but their directions will be opposite. Therefore, the net force on Q will be zero, as the forces cancel each other out.

- If q and -q are not equidistant from Q, i.e., r1 ≠ r2:
In this scenario, the magnitudes of F1 and F2 will still be the same, but their directions will depend on the relative distances of q and -q from Q. The net force on Q will be the vector sum of F1 and F2, taking into account their magnitudes and directions.

**Conclusion**

In conclusion, the total force on the charge Q when a charge -q is placed next to the charge q will depend on the relative distances of q and -q from Q. If they are equidistant, the net force on Q will be zero. If they are not equidistant, the net force will be the vector sum of the individual forces, considering their magnitudes and directions.

I think net force acting on Q will be zero because due to +q force is repulsive and due to - q force will be attractive respectively.. Thus these two forces will nullify each others effect..