instruction:
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
question:
The combustion of propane gas produces carbon dioxide and water vapor.
answer:
The combustion of propane gas produces carbon dioxide and what else?

question:
Amount of salt are aquatic biomes often classified.
answer:
How are aquatic biomes often classified?

question:
The oxygen atom in a water molecule pull the electrons away from the hydrogen atoms which leads to an unequal distribution of charge.
answer:
The oxygen atom in a water molecule pull the electrons away from the hydrogen atoms which leads to an unequal distribution of what?