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.