Correct Answer - B
Since the point `x=0` is a node and reflection is taking place from point `x=0`. This means that reflection must be taking place from the fixed end and hence the reflected ray must suffer an additional phase change of `pi` or a path change of `(lamda)/(2)`
So, if `y_("incident")=acos(kx-omegat)`
`impliesy_("reflected")=acos(-kx-omegat+pi)=-acos(omegat+kx)`