Here's why:

* Density of air: The density of air at standard temperature and pressure (STP) is approximately 1.2 kg/m³.

* Units: Density is typically measured in units of mass per unit volume (like kg/m³ or g/cm³).

While there might be other materials with densities close to 1.2 (depending on the units and conditions), air is the most common and likely material you're looking for.