Does anybody have an idea to if the use of a face mask is 100% safe like when you are at school for instance.

Not 100%

Explanation:

I assume you're talking about the mask in relation to coronavirus protection. Nothing except for staying home is 100% safe. It will lower your chances of contracting/spreading the coronavirus but there is still a chance that you might contract/spread it. You'll probably be okay as long as you don't touch your face, stay 6 feet apart and shower as soon as you get home.

c.) polymerase chain reaction

- "unlike the original dna fingerprinting method, dna profiling does not use restriction enzymes to cut the dna. instead it uses the polymerase chain reaction (pcr)? to produce many copies of specific str sequences. pcr is an automated procedure that generates lots of copies of a specific sequence of dna."