Which of the following observations would indicate that a material is a pure substance? O It does not dissolve in water.
O It changes color after heating.
O It cannot be physically broken down into different types of atoms.
O It can be physically broken down into different types of molecules
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C. It cannot be physically broken down into different types of atoms.

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.