Correct Answer - B
`x_1=Asin(omegat+phi_1)`
`x_2=Asin(omegat+phi_2)`
`implies|x_1-x_2|=2Asin(2omegat+(phi_1+phi_2)/(2))cos((phi_1-phi_2)/(2))`
To maximize `|x_1-x_2|`
`sin(2omegat+(phi_1+phi_2)/(2))=1`
`impliesasqrt2=2axx1xxcos((phi_1-phi_2)/(2))`
`implies(1)/(sqrt2)=cos((phi_1-phi_2)/(2))`
`implies((phi_1-phi_2)/(2))=(phi_1-phi_2)/(2)impliesphi_1-phi_2=(pi)/(2)`.
Hence (B)