Which of the following is NOT a clue that could indicate a chemical change? A. Change in color
B. Mixing of reactants
C. Change in energy
D. Release of a gas
E. Formation of a precipitate

i think its C, but im not 100% sure. if not c, then D, but C sounds more right.

Explanation:

everything else sounds like sure fire sighs of a chem change. good luck

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.

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.