Final answer:
The apostrophe is a punctuation mark that has two primary functions involving possession and contradictions. It is used to indicate possession with singular nouns or indefinite pronouns, and it also forms contractions.
Step-by-step explanation:
The punctuation mark that has two primary functions involving possession and contradictions is the apostrophe.
An apostrophe is used to indicate possession with a singular noun or an indefinite pronoun, such as 'Jack's brother' or 'everyone's favorite dessert'.
An apostrophe also forms contractions, such as 'can't' or 'it's'.