Is it obligatory to return the glass beakers that were distributed at the university, given that it was not announced that they must be returned? And is there a sin in using a pen found in a furnished apartment until its ink runs out?

Borrowed tools must be returned to the university. If the pen taken from the apartment is something people are lenient about, then there is no harm. However, if it has value and its owner would look for it, then it must be returned to him or his permission sought. If the owner is not known, then it is a lost item (luqatah).