The density of liquid oxygen is 1.141 g/mL, and the density of gaseous oxygen is 0.001429 g/mL. Therefore, 1 mL of liquid oxygen will produce 1.141 / 0.001429 = 800 mL of gaseous oxygen.

Therefore, to produce 2 liters of gaseous oxygen, we need 2000 / 800 = 2.5 mL of liquid oxygen.