Is rainwater a pure substance or a mixture?
rainwater can be considered a solution or a mixture.
Rain drops as they fall through the atmosphere will dissolve atmospheric gases. This makes rainwater a solution. All rainwater contains carbon dioxide
Raindrops as they fall through the atmosphere can also absorb particles of dust and other material. In there is a lot of particular materials in the air the rainwater will become a mixture. The dust and other particles do not dissolve into the rainwater so it remains a mixture not a solution.