Correct Answer - B
In air, a constant force `(= weight =mg)` will act on the ball. Therefore, the linear impulse can be obtained directly by multiplying this constant force with the given time interval. Further, this linear impulse is equal to the change in linear momentum. Thus,
`J=Fxxt=Deltap=mDeltav`
`implies Deltav=(t/m)F=(t/m)mg`
`=gxxt=(10m//s^2 dowonwards)(2s)`
`=20m//s` (downwards)