Answer:
It is "The opening of flask is pointed in an unsafe direction"
Explanation:
The students were there in the lab to perform practical without obeying the safety rules. The most reasonable basis for teacher's warning here, in this case, is the flask which is pointed in an unsafe direction. It is not specified whether the flask is containing any chemical or not but even if it is empty, it might just fall and break and create injury to anyone present in the lab because, the students are also not wearing proper laboratory wear in accordance to the safety rules which include lab coats, gloves, eyewear, etc. Also, some Students have not tied their hair and more importantly the flasks carrying liquids are not labeled. All of these things might end up in a critical situation for which the teacher warned students about it all.
Answer:
both inside and outside the nucleus
This is called a urinary catheterization.
