Why smaller particles scatter light of shorter wavelength more effectively than larger particles? And why larger particles scatter light of longer wavelengths more effectively than smaller particles? And why larger particles scatter light of every wavelength with equal effectiveness?

Dear student,
Shorter wavelength =More interactions with air per centimeter =more scattering

Larger wavelength= large gaps between the crests and troughs hence may skip touching the small air particles = but if given larger particles which can accomodate a complete long wavelength it bends the light and hence light scatters effectively by large or small particles because it provides larger area for interaction of light wavelength.