Answer:
F/32
Step-by-step explanation:
GIVEN
that the electrostatic force between sphere = F = kQq/r2
ANSWERED
Any time, third sphere touches the red or grey sphere the charges in it, will reduced to half, also, as half the charges are moved into the third sphere. That makes both spheres have equal charges (grounded) .
Also, the 3rd sphere tries to touch the grey sphere two times. Then, when we have initial charge in it to be Q, then, the final charge will be given has Q / (2x2) = Q/4
The similarly with the red sphere, has the initial charge was q, so we have last charge after the third sphere has touches it three times = q/(2x2x2) =q/8
Therefore,given that the new coulombs force = kQq/(r2x4x8) = F/32