One charge is decreased to one-third of its original value, and a second charge is decreased to one-half of its original value.

By Coulomb’s law, the force is proportional to the product of the two charges. Reducing one charge to one-third and the other to one-half changes the force by (1/3) × (1/2) = 1/6. So the force decreases to one-sixth of its original value, choice C.

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