Is radon testing required when I sell my house?

In some states or local areas, radon testing may be required. Check with your local Board of Realtor, or your state department of environmental quality. While radon testing may not be required, the U.S. Environmental Protection Agency (EPA) recommends conducting a radon test prior to putting a house on the market, and if necessary, lowering radon levels in the house. Positive test results can be a positive selling point.
Find more by looking at the EPA Home Buyer’s and Seller’s

Mold is natural, so what's the big deal?

Molds are natural and generally pose no adverse health effects outside the home. However, mold indoors can be an indoor air issue. Mold produces spores that become airborne. These spores and mold fragments are introduced into the respiratory system, where they can cause allergic reactions, trigger asthma attacks, and cause other health problems. EPA A Brief Guide to Mold and Moisture Control . See also Healthy Homes Partnership