ans is C
e.g R1=(a,b,c,d) R2=(c,d,e,f)
R1-R2=(a,b) , R2-R1=(e,f)
R1 ∩ R2 =c,d
c,d is common to both relation ,now to be lossless c,d must be a superkey in at least one of the relation R 1 and R 2
acc to option C it is superkey in both relation so it is lossless