Correct Option (B)
Diffusion of light in the atmosphere is primarily caused by thescattering of light by suspended particles.Dust particles, being larger than individual gas molecules, effectivelyscatter visible light in various directions. This phenomenon, known asscattering, leads to the diffusion of sunlight, illuminating areas not in direct sunlight and contributing to the general brightness of the sky.
Incorrect Options
- Carbon dioxide: While a significant greenhouse gas, carbon dioxide molecules are too small to cause substantial scattering of visible light.
- Helium: Helium is an inert gas with very small atomic size, making its contribution to the scattering or diffusion of visible light negligible.
- Water vapours: Water vapour molecules are also too small to significantly scatter visible light. While water droplets (e.g., in clouds or fog) can scatter light, water vapour itself does not cause the widespread diffusion attributed to dust.