Socony-Vacuum was formed in 1931 by the merger of Standard Oil of New York and Vacuum Oil.
Standard Oil of New York was commonly called Socony, an abbreviation derived from its corporate name. Vacuum Oil, founded in 1866, was especially well known for Mobiloil, an early branded automotive lubricant. Their combination created Socony-Vacuum Corporation, joining Socony’s petroleum interests with Vacuum’s lubricants and distribution business.
The new company remained an important international oil producer and marketer. In 1933, Socony-Vacuum combined its Far Eastern interests with those of Standard Oil of New Jersey in a 50–50 joint venture called Standard-Vacuum Oil, commonly known as Stanvac. Socony-Vacuum itself later changed its name to Socony Mobil Oil in 1966.
That lineage explains why the answer is sometimes confused with Mobil. Mobil was the later brand and corporate identity, not the name created by the 1931 merger. The other choices—Gulf Oil, Atlantic Richfield and Standard Oil of Ohio—were separate companies with different histories.