How many atoms of oxygen are there in 4.4g of CO_{​​​​​2}

Molar mass CO2 = 44 g/mol
You have 4.4g , so you have 4.4/44 = 0.1 mol CO2
1mol CO2 has 6.022*10^23 molecules
0.1mol CO2 has (6.022*10^23)*0.1 = 6.022*10^22 molecules
1molecule of CO2 contains 2 atoms of O
Therefore, 6.022*10^22 molecules of CO2 will contain (6.022*10^22) *2 = 1.204*10^23 atoms O

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