Translation:There are twenty students in the classroom.
A. The comments are for learners to ask or answer. The staff read the reports from the REPORT BUTTON.
B. Class is not "used more" than classroom. Class refers to the course or collection of students, while classroom means the room. Each is used according to the meaning.
Because "aula" uses "el" even though it is feminine. https://www.spanishdict.com/answers/196352/el-aula-o-la-aula