How many oxygen atoms are in 17.63 grams of co2?

CO₂ = 12 + 2*16 = 44 g/mol

1 mole of CO₂ contain an Avogadro number of molecules of CO₂

44g of CO₂  contain 6.02 * 10²³ molecules of CO₂

17.63g of CO₂ will contain:
                                                17.63 * 6.02 * 10²³ /44
                                         
                                                ≈ 2.412 * 10²³ molecules of CO₂

Note: 1 molecule of CO₂ has 2 atoms of O

2.412 * 10²³ molecules of CO₂ will have 2.412 * 10²³ * 2 = 4.824 * 10²³ atoms of O.

 4.824 * 10²³ atoms of O.