why is it that O3 floats above O2?

Answer 1

It doesn't. An UV-B photon strikes a molecule of O2, dissociating it into two energetic O atoms. These atoms in turn collide with other O2 molecules, latching with them to produce O3. If not involved in collisions with other molecules, the O3 decays with a half- life of about 21 hours, kicking off an O atom. Again, with no intermediate collisions, 2 O atoms will collide and latch, forming O2. As all this occurs in a relatively narrow band in the upper stratosphere we have the illusion of an O3 layer floating on lighter O2 and N2.

Answer 2

Here is what i think:
Density is defined as mass over volume, and O2 is denser than O3, thus O3 is found in the upper levels of the atmosphere.

Answer 3

It doesn't. Ozone is created from diatomic oxygen by ultraviolet light. This happens high in the atmosphere, so there is more O3 up there.