Correct Answer - b., c., d.
`(Deltaphi)/(2pi)=(Deltax)/(lambda)`
`Deltax=(lambda)/(2pi)Deltaphi`
`=(lambda)/(2pi)pi=(lambda)/(2)`
let for P: `y_(1)=A sin omega t`, then
For Q: n`y_(2)=A sin(omega t-pi)=-A sin omega t`
we see that `y_(1)=-y_(2)`
and `|y_(1)|=|y_(2)|`
Frequency of both particle should be same because the same wave passes through them.