You are given 4.4g of CO_2 gas. To calculate the molecules of CO_2 present, you need to first covert from grams of CO_2 to moles of CO_2.
4.4g CO_2 *(1 mol)/(44.1g)= .10 mol of CO_2
After you covert to moles of CO_2, you then covert to molecules of CO_2 with Avogadro's number; 6.022 * 10^23,
.1 mol CO_2 (6.022*10^23)/(1 mol)= 6.0*10^22 molecules of CO_2
to do all your conversion in one step;
4.4g CO_2 (1mol)/(44.1g) (6.022*10^23)/(1mol)= 6.0*10^22 molecules of CO_2
To determine the atoms of oxygen present;
You are given 4.4g CO_2, but this time we want atoms (or molecules) of Oxygen gas.
4.4g CO_2* (1mol)/(44.1g)= .10 mol CO_2
For every mol of CO_2, there is 1 mol of oxygen (O_2)
.10 mol CO_2 (1mol O_2)/(1mol CO_2)=.10 mol O_2
we use Avogadro's number again;
.10 mol O_2 (6.022*10^23)/(1mol O_2)= 6.0*10^22 molecules/atoms O_2
All worked out;
4.4g CO_2 (1mol CO_2)/(44.1g CO_2) (1mol O_2)/(1mol CO_2) (6.022*10^23)/(1mol O_2)= 6.0*10^22 molecules of O_2