The correct option is B S1,S3,S4 and S6
For surface z=0 on xy plane,
Normal →S4=l2(−^k)
For surface z=l on xy plane,
Normal →S2=l2(^k)
For surface x=0 on yz plane,
Normal →S6=l2(−^i)
For surface x=l on yz plane,
Normal →S5=l2(^i)
For surface y=0 on xz plane,
Normal →S1=l2(−^j)
For surface y=l on xy plane,
Normal →S3=l2(−^j)
Electric field →E=−5x^i+3z^k
Flux ϕ=→E.→A
ϕ4=−3l2z=0
ϕ2=3zl2=3l3
ϕ6=5l2x=0
ϕ5=−5l2x=−5l3
ϕ1=0
ϕ3=0
So the surfaces which have zero flux are S1,S3,S4 and S6.