Air is transparent because:
Air allows all the light that falls on it to pass through.
We can see any object around us because light reflected from an object can move through space and reach our eyes. Once light reaches our eyes, signals are sent to our brain and our brain deciphers the information in order to detect the appearance, location, and movement of the objects we are looking at.
Since air is made up of gases which allow all the light that falls on it to pass through, no light is reflected by the air hence we are unable to see air.
Air allows all the light that falls on it to pass through it, is the correct reason for air to be not visible to us.