The answer which shows proper comma usage is option A. "Mexico’s full name is the United Mexican States, and it is known as Estados Unidos Mexicanos in Spanish."
A comma should be use:
before any coordinating conjunction (and, but, for, or, nor, so, yet) that links two independent clauses;
after a dependent clause that starts a sentence;
to offset appositives from the rest of the sentence,
to separate items in a series,
after introductory adverbs,
when attributing quotes,
o separate the elements in a full date (weekday, month and day, and year). Also separate a combination of those elements from the rest of the sentence with commas.