Option (b) Dust particles is correct. The textbook explicitly states under the 'Dust Particles' section that the atmosphere contains small solid particles 'which may originate from different sources and include sea salts, fine soil, smoke-soot, ash, pollen, dust and disintegrated particles of meteors.' All the items listed in the question — sea salt, pollen, ash, smoke soot, and fine soil — are directly mentioned as components of dust particles. These are solid particles suspended in the atmosphere, not gases, water vapour, or meteors themselves.