How many mol of Oxygen are in 45.9 grams of CO2?

Answer 1

I assume you mean how many moles of oxygen ATOMS are in .....
moles CO2 = grams CO2/molar mass CO2.
You see there are 2 oxygen atoms in a molecule of CO2; therefore, 2x moles CO2 will be moles oxygen atoms. If you meant how many moles of O2 MOLECULES are in ..., then 1/2 of the mols O atoms will be moles O molecules.

Answer 2

45.9 mol of co2