Which stays the same during chemical reactions?
the overall types of atoms only
the overall numbers of atoms only
both the overall types and numbers of atoms
neither the overall types or numbers of atoms

Both the overall types and numbers of atoms stay the same during chemical reactions.

since electrons are negative the answer is neagtaive

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.