The usual cause is when air is holding the maximum amount of water possible.
Typically, yes. As air rises it cools, which can cause moisture in it to condense.
Saturated air is air that has all the water vapor that it can hold.
This will cause condensation. You could get a cloud or dew.
Saturated air is air that has all the water vapor that it can hold.
There is not enough information to determine this. Just being at sea level does not cause the air to have a specific saturation (humidity).
Saturated air is more dense.
When a parcel of air is saturated with water vapor the relative humidity of that parcel of air is 100%.
more air
100%
more air
When a paracel of air is cooled to the temperature at which it is saturated, it has reached its dew point.
If it is humid it is saturated. If it is dry it is unsaturated.