The mass of its envelope ("skin") plus the mass of the gas inside. If this mass is less than the mass of air displaced by the balloon's volume the balloon will ascend if it isn't tethered.
Free range eggs are definatly more than cooped eggs. The average is about £2.00 for a pack of 8. It varies at different supermarkets. Supermarkets own are just as tasty but just a little bt less!