Which activist was most instrumental in the passage of the nineteenth amendment?

The correct answer is Susan B. Anthony.

Susan Brownell Anthony (1820-1906), was born on February 15, 1820, in Adams, Massachusetts. She was one of the most important supporters of the women's suffrage movement. She and Elizabeth Cady Stanton, visited many cities of the United States to deliver speeches, supporting the movement.

In 1848, Anthony and other women were part of first "Women's Rights Convention" in the U. S. in Seneca Falls, New York.

Her activism made her an instrumental part in the passage of the 19th amendment, although she died in 1906. Women were given the right to vote with the 19th amendment that was passed in 1920.

Susan B Anthony is the correct answer