Ethan is observing chemical and physical properties of a substance. He heats a substance and observes that the substance turns from a brown solid to a black powder. He refers to several chemistry journals that claim this represents a chemical reaction. From his observation and research, he concludes that the substance goes through a chemical change when heated. How can Ethan best defend his conclusion?

A by demonstrating that the substance will eventually melt if the temperature continues to increase
B by verifying that the substance is now made up of different molecules than before it was heated
C by verifying that the substance is made up of only one type of element
D by demonstrating that the substance is less dense after it is heated

The answer is B

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your answer?

B by verifying that the substance is now made up of different molecules than before it was heated

The best way for Ethan to defend his conclusion that the substance undergoes a chemical change when heated is by verifying that the substance is now made up of different molecules than before it was heated.

Answer choice B states that Ethan should verify that the substance is now made up of different molecules. This is the most appropriate choice because a chemical reaction involves the rearrangement of atoms to form new substances with different chemical properties. If the substance is made up of different molecules after being heated, it suggests that a chemical reaction has occurred.

Answer choice A, demonstrating that the substance will eventually melt if the temperature continues to increase, is not sufficient for defending the conclusion. Melting is a physical change where a substance changes from a solid to a liquid state, but it does not necessarily imply a chemical reaction has taken place.

Answer choice C, verifying that the substance is made up of only one type of element, is unrelated to the observation that the substance turns from a brown solid to a black powder when heated. It does not provide evidence for a chemical change.

Answer choice D, demonstrating that the substance is less dense after it is heated, is also unrelated to the observation and does not provide evidence for a chemical change. Density is a physical property that can change without indicating a chemical reaction.