Keep the seed with it. For guacamole, place the seed in the middle of the bowl. For chopped avocado, make sure it's stored in an airtight container along with the seed. I don't know why it works but it does.
Added 11/15/09: It works because there are enzymes within the seed that prevent the avocado from turning brown.
http://www.articlesbase.com/food-and-beverage-articles/keep-apple-slices-from-turning-brown-naturally-1238490.html
sprinkle with lemon juice
Yes it should. Potatoes turn brown when exposed to air. Covering them with any liquid should keep them from turning brown.
To keep them from drying out and turning brown
you don't
cause it gets pooped on
Lime juice
Oxygen. Dip apple slices in lemon juice to keep them from turning brown.
A hypothesis doesn't have to be a correct statement. Just pick a chemical and say this one will or will not keep the fruit from turning brown. Then give a brief statement about why you think this way.
keep it in the frige
will covering peeled potatoes in olive oil keep them from turning brown
Use lemon juice.