Answer
1.43 g/L 2.14 g/L
Work Step by Step
density = molar mass x p / RT
At STP ( p = 1 atm and T = 273 K)
Molar mass O2 = 32 g/mol
density = 32 x 1 / 0.0821 x 273 = 1.43 g/L
molar mass O3 = 48 g/mol
density = 48 x 1 / 0.0821 x 273 = 2.14 g/L