Answer: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)