You should remember the formula that relates density, mass and volume such that:

`rho = m/V`

`rho` represents the density

m represents the mass

V represents the volume

Since the problem requests to evaluate the density of gaseous `O_2` , you should remember that the volume of a mole of an ideal gas at standard temperature and pressure is of 22.4 L.

You need to evaluate the molar mass of `O_2` such that:

`m= 2*16 = 32 g`

Substituting 32g for m and 22.4 for V yields:

`rho = 32/22.4 = 1.428 g/L`

**Hence, evaluating the density of gaseous `O_2` at standard temperature and pressure yields `rho = 1.428 g/L` .**

at stp volume is 22.4dm3 hence:

d=m/v

mass=16x2

mass=32;

d=32/22.4

ans=1.42g/dm3

p=m/v

p represents the density

m represents the mass

V represents the volume

1.428g/l