If n identical water drops assumed spherical each charged to a potential difference U coalesce to a single drop, the potential energy of the single drop is (assume that drops are uniformly charged):plzz explain

1. n^(1/3) U
2. n^(2/3) U
3. n^(4/3) U
4. n^(5/3)U

Volume of n drops = volume of bigger drop 

n  4/3 pi (r)^3  = 4/3 pi (R)^3

Therefore ,  R = ( (n)^1/3) r 

also charge remains conserved 

charge on 1 drop = q 

charge on big drop containing n drops = (nq) 

Therefore potential on big drop = K (nq)/ ((n)^1/3)r