Answer:
It will decrease to one-sixth the original force.
Step-by-step explanation:
The electrical force is given by :
..............(1)
Where
k is the electrostatic constant
r is the distance between charges
One charge is decreased to one-third of its original value, and a second charge is decreased to one-half of its original value.
i.e.

and

New force is given by :


So, the new force will decrease to one-sixth the original force. Hence, the correct option is (c).