Which of the following is not a laboratory safety rule?

Most incidents in chemistry labs can be prevented by taking a few simple safety precautions, being aware, and being mindful. It's crucial to keep in mind that a worker's safety in a lab is influenced by both his or her own actions and those of their coworkers. There are many rules or systems to obey in a laboratory. 

The first option can't be chosen as correct because not all the given options are valid safety rules.
The second option, acid can't be mixed with a base, is not a safety rule. While doing experiments different types of acid-base mixing take place.
Third, when diluting acids, the acid must be poured into water to avoid an exothermic reaction. It is a lab safety rule.
The last option is also a lab safety rule. One should tie their hair before entering the lab to avoid accidental burns.
Thus acid can't be mixed with base is not a lab safety rule.

Hence, the correct answer is option B.