A charge Q is divided into two parts, q and (Q - q). The repulsion between them is maximum when Q : q is

2 : 1 1 : 2 4 : 1 1 : 4

2 : 1

Force between two charges are $ F = \frac{1}{4\pi\epsilon_0}\frac{q(Q-q)}{r^2}$ For Force to be maximum $ \frac{dF}{dq} = 0$ $\Rightarrow Q - 2q=0 \Rightarrow Q:q = 2$