Well when a particle of air is becomes heated it rises, right? So you could write some like you started off close to the earth (aka the troposphere) until you became heated then you started to rise and as you reached higher elevations you cooled down and you were recycled into cool air and you moved back down and became new fresh cool air until the next time you'll become heated and rise again to be recycled into fresh cool new air.
The properties of the components of substance are different. One component has magnetic properties, another does not. So, we have at least 2 individual substances that were mixed together. So, we have a mixture.
