Following on the sucessful activism of Cesar Chavez, Mexican American youth began to refer to themselves as

a. Mexicans.
b. Los Barrios.
c. Los Hombres.
d. Chicanos.

To find the answer to this question, we can start by understanding the context and the history behind it. Cesar Chavez was an American labor leader and civil rights activist who co-founded the National Farm Workers Association, which later became the United Farm Workers (UFW) union. He was a prominent advocate for the rights of Mexican American farmworkers and played a crucial role in improving their working conditions and wages.

During this time, a cultural and political movement known as the Chicano Movement emerged. It sought to empower Mexican Americans, promote their civil rights, and celebrate their cultural heritage. This movement aimed to redefine the identity of Mexican Americans by reclaiming and redefining the term "Chicano."

So, the answer to the question is:

d. Chicanos.

After the activism of Cesar Chavez and during the Chicano Movement, Mexican American youth began to refer to themselves as Chicanos to express their pride in their Mexican heritage and assert their distinct identity within American society.