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