Two identical conducting spheres $$P$$ and $$S$$ with charge $$Q$$ on each, repel each other with a force $$16 \text{ N}$$. A third identical uncharged conducting sphere $$R$$ is successively brought in contact with the two spheres. The new force of repulsion between $$P$$ and $$S$$ is :

Initial: P and S each have Q. Force = $$kQ^2/d^2 = 16$$ N.

R (uncharged) touches P: charge on each = Q/2. Then R (Q/2) touches S (Q): charge on each = 3Q/4.

New charges: P = Q/2, S = 3Q/4.

Force = $$k(Q/2)(3Q/4)/d^2 = \frac{3}{8}kQ^2/d^2 = \frac{3}{8}×16 = 6$$ N.

The correct answer is Option (2): 6 N.

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