KCET 2010 Physics Solved Paper

Two small spheres of masses M1 and M2 are suspended by weightless insulating threads of lengths L1 and L2. The spheres carry charges of Q1 and Q2 respectively. The spheres are suspended such that they are in level with one another and the threads are inclined to the vertical at angles of θ1 and θ2 as shown. Which one of the following conditions is essential, if θ1=θ2 ?