What are the number of moles of CO2 which contain 8.0 gram of oxygen?

Moles of oxygen = 8/16 = 0.5
For two moles of oxygen, CO2 = 1 mole
For one mole of oxygen, CO2 = 1/2 mole
For 0.5 moles of oxygen, CO2 = 1/2 × 0.5 = 0.25 moles