Final answer:
The correct answer is d. Closer to one charge, negative, when two identical point charges, q each, are kept 2 m apart in air. A third point charge q of unknown magnitude and sign is placed on the line joining the charges such that the system remains in equilibrium.
Step-by-step explanation:
To find the position and nature of the unknown charge q, we need to consider the equilibrium condition.
When the system is in equilibrium, the net force on q is zero.
Since the two identical charges are placed 2 m apart and are in equilibrium, the unknown charge q must be placed at the midpoint between the two charges.
Now, to determine the nature (positive or negative) of the charge q, we need to consider the principle of electrostatics. Like charges repel each other, while opposite charges attract each other.
Since the system is in equilibrium, the unknown charge q must have the opposite sign (negative) compared to the two identical charges in order to balance out the forces and maintain equilibrium.
Therefore, the position of q is at the midpoint and its nature is negative.
The unknown charge q is placed at the midpoint between the two identical charges and has a negative nature.