The atmosphere always has:

Correct answer: (d) All of the above

Explanation

The atmosphere is a mixture of gases (the air) with suspended solid and liquid particles:

• air is mostly nitrogen (about 78%) and oxygen (about 21%), with argon, carbon dioxide and other gases;
• oxygen is always present and keeps living things alive and supports burning;
• dust particles (aerosols such as salt from the sea, fine soil, smoke and pollen) are found in the lower layers; water vapour condenses round them to form clouds.