According to the Avogadro's law , equal number of moles of gases occupy the same volume at identical conditions of temperature and pressure. Even if we have a mixture of non-reacting gases then Avogadro's law is still obeyed by assuming mixture as a new gas.
Now let us assume air to consist of 80% by volume of nitrogen `(N_(2))` and 20% by volume of oxygen `(O_(2))` . If air is taken at STP , then its 1 mol would occupy 22.4 L . 1 mol of air would contain 0.8 mol of `N_(2)` and 0.2 mol of `O_(2)` hence the mole fraction of `N_(2)` and `O_(2)` are given by `X_(n_(2))=0.8, X_(o_(2))=0.2`
If air is treated as a solution of `O_(2)` and `N_(2)` , then % w/w of oxygen is:

Options

A. `(10)/(9)`
B. `(200)/(9)`
C. `(700)/(9)`
D. `(350)/(9)`

Answer

B