Answer:
• One mole of oxygen is equivalent to 16 grams.
→ But at STP, 22.4 dm³ are occupied by 1 mole.
[tex]{ \tt{22.4 \: {dm}^{3} \: \dashrightarrow \: 16 \: grams}} \\ { \tt{33.5 \: {dm}^{3} \: \dashrightarrow \: ( \frac{33.5 \times 16}{22.4} ) \: grams}} \\ \\ \dashrightarrow \: { \boxed{ \tt{23.94 \: g \approx \: 24 \: grams}}}[/tex]