calculate the no of oxygen atoms present in 4.4 g of CO2

Molar mass CO₂ = 44 g/mol
Therefore, number of moles in 4.4 g CO₂ = 4.4/44 = 0.1 mol

Now,
1mol CO₂ contains 6.022 x10²³ molecules
0.1mol CO₂ contains 6.022 x 10²³ x 0.1 = 6.022 x 1022²² molecules

Also,
1molecule of CO2 contains 2 atoms of oxygen
Therefore,

6.022 x10²³ molecules of CO₂ will contain 6.022 x 10²² x 2 = 1.204 x 10²³ atoms of oxygen