The distance estimation for which ray optics is good approximation for an aperture of 3 mm and wavelength 300 nm would be:

30 m

The correct answer is Option (2) → 30 m

The angular width (θ) of the central diffraction maximum (for the operator) can be estimated -

$θ≃\frac{λ}{d}$

$λ$ = Wavelength of light = 300 nm

d = Aperture size = $3mm = 3×10^{-3}m$

$θ≃\frac{300×10^{-9}}{3×10^{-3}}=10^{-4}$ Radians

Also, 

Distance, $D>>\frac{d}{θ}=\frac{3×10^{-3}}{10^{-4}}=30m$