Correct Answer - b
`lambda=2(4.5-2.5)=4 cm, v=nlambda`
`rArr n=(40)/(4)=10 Hz`
`phi=(2pi)/(lambda)Deltax=(5pi)/(4)rad implies phi=(2pi)/(T)Deltat`
`Deltat=(phi)/(2pin)=(pi//3)/(2pi10)=(1)/(60)s`
velocity of `p` should be maximum, as it is at mean position.
`v_(p)=omegaA=2pifA=2pixx10xx(2)/(100)`
`=1.26 m//s`
this velocity should be `-ve`, because slope at `p` is `+ve`.