a) It's only 10 percent of them that do so. OK
b) Only 10 percent of them do so. OK
c) There are only 10 percent of all the pupils who do that. No
d) These are only 10 percent of them. No
e) These bullies only represent 10% of the pupils. Not really. The bullies don't represent themselves.
f) It's only 10 percent who bully others. OK
Student or Learner