The correct answer is The purpose of a bibliographic card in the index-card method of note-taking is to record (b.) MLA-style source information.
A bibliographic card is a card in which the author who has written a work used as a source for information for a research is given credit. When writing a bibliographic card it is necessary to include the following information: author of the source, 2) title of the source, 3) city of publication, 4) publisher, 5) year of publication. For instance, the bibliography card in the index card for William Burns’ book A Brief History of Great Britain should be:
Burns, William. A Brief History of Great Britain. New York, Facts on File, 2010.