Question

the number of moles of carbon dioxide which contain 8 g of oxygen is

Answer 1

1 mole of carbon dioxide have 32g of Oxygen.
So 8 g Oxygen will be found in 1/4 mole of carbon dioxide or 0.25 mole

Answer 2

Hey,

refer to image attached.

$1.5 \times 10 {}^{23}$
molecules will have 8gms. of Oxygen that means, 0.25 moles will have 8 gms. of oxygen

HOPE THIS HELPS YOU.