In engel v. vitale, the supreme court decided that prayer in school a) was protected under freedom of speech. b) violated the right to privacy. c) violated freedom of religion. d) was protected under freedom of expression.

The correct answer is:  [C]:  "violated freedom of religion" .
 
→  {Note:  in the sense that "mandated" and/or:  "encouraging/ pressuring/ suggesting/incorporating/insisting/focusing" on "religious praying" in school violated the "freedom of religion" .}.

Correct answer for apex is d.