How many significant figures are in 0.723 m

Why is permeable soil best for plants that need a lot of drainage?

Why does earth rotate? because earth is formed from cold gases collapsing due to gravity because the matter in the nebula that formed earth was spinning because earth forms more than 99% of the mass of the solar system because the hydrogen atoms inside the nebula fused to form helium

How does science use models to gain a better understanding of concepts?