The correct choice is (a) σx= σx’+γw(h-he)
For explanation I would say: The total stress is equal to effective stress plus pore pressure. In x- direction, the normal stress is given by,
σx= σx’+u
u= γw(h-he)
where, h=total head at the point
he=elevation head
∴ σx= σx’+γw(h-he).