Ray optics is based on the assumption that light travels in a straight line . Diffraction effects observed when light propagates through small apertures / silts or around small obstacles ) disprove this assumption , yet the ray optics assumption is so commonly used in understanding location and several other properties of image in optical instruments? what is the justification ?

Question

$\begin{array}{1 1} \text{Size of the obstacle is very much lesser than the wave length of light } \\ \text{Size of the obstacle is larger than the wave length of light } \\ \text{Size of the obstacle is equal to the wave length of light } \\ \text{None of these } \end{array} $