If there is not one scientific method, then what do all scientists have in common??? Plsss I will give brainliest, and 12 points !!

One thing that all scientists have in common is that they find problems in the world, and attempt to seek answers to those problems. Everything that scientists do begins with observations, leading to questions.

Let me know if this helps!

All scientist try to find the problems in nature and seek to find the answers

0.40 atm

How did we get 0.40?
Use the formula of Dalton's Law of partial pressure. 
Work it out by substituting the given values.
Given:
Total gas exerted by nitrogen- 80%
Total pressure- 2.0 atm
pressure of oxygen-?
P denotes total pressure exerted by nitrogen and n denotes total pressure of the mixture.
Poxygen = P/n
             = 0.8 /2.0
             = 0.4

(80 % is changed into decimal number, 0.8)