Which substance is a source of radon-222 in or around the home? 

A)  furniture stuffing 
B)  foam insulation 
C)  dry-cleaning fluid fumes on clothes 
D)  soil surrounding the foundation

Radon-222

A radioactive, colorless, odorless, tasteless noble gas, occurring naturally as an indirect decay product of uranium or thorium, and considered a health hazard due to its radioactivity.

Soil Surrounding

The layer of the Earth's crust that covers its surface, in which plants grow and where various organisms can live.