If you place a balloon over the neck of an empty 2 liter bottle, how can you make it inflate?
By empty, I assume you mean nothing in the bottle other than air. If so, you could squeeze the bottle or heat the bottle (gently so you don't melt the bottle) You could blow in the balloon and inflate it inside the bottle (although it would be difficult to stop it from deflating)
If it is truly empty, you can't. If it contains air, all you have to do is heat it.
Fart in the bottle and stretch the balloon over the opening. Now put it in the Sun on the counter and wait for your sister to find it.
Science puzzle? Put the bottle in very hot water; the air will expand and inflate the balloon a bit.
Have vinegar in the bottle and baking soda in the balloon.
Dances with Weed
Squeeze the bottle. So yes
blow in it
Add some Memtos and Coke to the bottle. The gas will inflate the balloon.