F∝x2QAQCx is distance between the spheres. After first operation charge on 2Q is halved i.e 2Q. and charge on third sphere becomes C. Now it is touched to C, charge then equally distributes them selves to make potential same, hence charge on (Q+2Q)21=43Q becomes ∴Fnew∝x2QCQB=x2(43Q)(2Q)=83x2Q2Fnew=83For, 8F