How does a polar covalent bond differ from a nonpolar covalent bond?

a. in a polar bond, electrons are shared unequally.
b. in a polar bond electrons are transferred
c. a polar bond is always stronger
d. a polar bond only occurs with atoms of the same element.

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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.