Q&A for How to Store Onions

You can, for a certain amount of time. You should put it in an airtight container and keep it in a vegetable drawer if you have one. You may also consider purchasing an onion saver.

It kind of depends on room temperature, how long it was left out and so forth, but onions don't go bad very quickly. If the onion has gone bad, you should be able to spot mold, discoloration, sliminess, etc.

It depends on if they are chopped or not.

True fruit flies are only interested in eating yeasts that grow on fruit. The onions must have been too moist and allowed yeast to proliferate. Try drying the onions more thoroughly, or use a less sweet variety. Also, see the various WikiHow articles on controlling fruit flies.

You could, but they won't have the crispy quality people like in salads.

Do not store onions and potatoes near each other, as they will spoil sooner.

You can store them in your basement, but not in an old laundry bag. Store them in a Ziploc.

You can dice the onions and store them in the freezer.

If it smells okay and there is no visible mold on it then it should be safe. It may be a little dry or rubbery though.

Yes, but the onion will dry up in around 72 hours. To avoid this, do not grind it before freezing -- just grind it when you need it.

No, you do not.