If eight charged same water drops each with a radius of 1mm and a charge of 10−10C  merge into a single drop. Then the potential of the big drop is

r be the radius of small dropR be the radius of big dropvolume is conserved so Vbig=8 Vsmall43π R3 = 8× 43πr3⇒R= 2rpotential of big drop is Vbig= 14πε0 8qr put q and r values in the above equation we get V = 3600v