When water freezes into ice, some of the properties have change. What stays the same.
Answer: 1: Ice Melting is a physical change. When liquid water (H2O) freezes into a solid state (ice), it appears changed; However, this change is only physical as the the composition of the constituent molecules is the same: 11.19% hydrogen and 88.81% oxygen by mass.
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The amount of energy required to change the temperature or phase of a reactant
The troposphere protect the molecules because there are higher layers on top. This makes life possible on Earth.