Ans will be C
conflict serializable means we can first run one Transactioon then after it second without any conflict
conflict occurs when data item is same and at least one operation is read
so for S1 r1(X); r1(Y); r2(X); r2(Y); w2(Y); w1(X)
here w1(x) can not be placed before r2(X) as data item is common(X) and one operation is write so it is not conflict serializable
now for S2 r1(X); r2(X); r2(Y); w2(Y); r1(Y); w1(X)
here r1(X) can be placed after w2(Y) as data item is different and before that only read operation are there so it is conflict serializable as T2 can be executed before T1