Select the word from the list that best fits the definition the most common gas in the atmosphere.

Nitrogen

Explanation:

Nitrogen is the most gas as it is the most abundant gas in atmosphere. It constitutes nearly 78% of the earth's atmospheric gases composition. After nitrogen, oxygen is the second most gas followed by carbon dioxide and other rare gases (only 1%).  

Atmosphere consists of some amount of water vapor (1%). Small particles like aerosols, dust, spores and pollen, volcanic ash, smoke, etc. are also found