How do the densities of the planets support the nebular theory?

Explanation:

According to this theory, the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust. This could have been the result of a passing star, or shock waves from a supernova, but the end result was a gravitational collapse at the center of the cloud.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

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