Should I advise students who place their books on the floor beside their feet during exams, for fear that someone might step on them, even though this is common and I have not seen anyone accidentally step on a book?

Placing religious books on a pure and clean floor is permissible and not considered disrespectful, especially if no elevated place is available for them. Placing non-religious books is even more permissible. Therefore, one should not condemn someone who does this. The questioner, who appears to be suffering from waswas (obsessive whispering), is advised to disregard it, stop dwelling on it, refrain from asking about it, turn to Allah in supplication, and consult psychiatrists; because an abundance of questions does not cure waswas, but rather increases it.