Final answer:
Water synthesis from H2 and O2 is a chemical change, while boiling and melting water are physical changes.
Explanation:
Chemical: The synthesis of water (H₂O) from hydrogen gas (H₂) and oxygen gas (O₂) involves breaking the existing bonds between O and H in their respective gases, and forming new bonds between H and O to create water. This represents a chemical change.
Physical: Boiling and melting water are physical changes where no new bonds are formed or broken. For example, when water boils, it transitions from a liquid to a gas without any chemical bond changes.
Physical: Ice melting into water and turning into steam are physical changes as the composition of the water molecules remains the same throughout these phase changes.
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