Identifying the confounded effect from a $2^4$ block split via sign parity

In a $2^4$ factorial design with two blocks of 8 plots each the treatment combinations are allotted as: Block I: $a,b,ac,bc,d,abd, cd,abcd$; Block II: $1,ab,c,abc,ad,bd,acd,bcd$. Hence the confounded treatment combination is: