One of my house plants is very sick. It has a white mold look on its leaves. What is wrong? How can I save it?

it sounds like mealy bugs don't panic...I get it sometimes. Get a spray bottle in the house hold cleaning section and fill it up about an inch with rubbing alcohol and the rest with water. Cover up the base, I put a shopping bag over the soil so it can't get wet, and I spay and spray it paying close attention to under the leaves and where the fuzzy stuff is mostly located. Do this about two or three times a week for a couple of weeks, then cut it down to once a week or so.
If you have area's that are heavily infested, dip a cotton swab in the rubbing alcohol and wipe it away.
Let us know how it works out for you.
BJ