The molecular mass of CO₂ and O₂ are approximately 44 and 32 respectively. Which of the following statements regarding the mass of oxygen and number of molecules of oxygen is correct?

P. The mass of oxygen in 2.24 litres of CO₂ is 3.2 g

Q. The number of molecules of oxygen present in it is 6.022 x 10²³

1. Only P
2. Only Q
3. Both P and Q
4. Neither P nor Q

Only P

Reason —

P: As 22.4 L of CO₂ at S.T.P. has mass = 44 g

Therefore, 2.24 L of CO₂ at S.T.P. has mass = $\dfrac{44}{22.4}$ x 2.24 = 4.4 g

44 g of CO₂ has 32 g of oxygen

So, 4.4 g of CO₂ will have = $\dfrac{32}{44}$ x 4.4 = 3.2 g of oxygen.

Hence P is correct.

Q: No. of moles of O₂ in 3.2 g = $\dfrac{3.2}{32}$ = 0.1 g .

1 mole of O₂ = 6.023 x 10²³ molecules

0.1 moles has molecules = 6.023 x 10²³ x 0.1 = 6.023 x 10²²

Hence Q is incorrect.