heres an easy solution
A) 1 and 4 are not isomorphic (iv has 3-length cycle but i does not)
D) similarly 2 and 4 are not isomorhic(ii does not have 3-length cycle)
C) also 1and 3 are not isomorphic( iii has 5-length cycle which is absent in i)
so A,C,D are are wrong, remaining is B which must be the answer. comment if you find any thing wrong