Answer:
3.0 dm^3 of sulphur trioxide is formed
Step-by-step explanation:
From Gay Lussac's law of combining volumes;
The equation is;
SO2(g) + 1/2O2(g) ------> SO3(g)
Reacting volumes 1 vol 1/2 vol 1 vol
Initial volumes 3.0 dm^3 2.0 dm^3 0.0 dm^3
Final volumes 0.00 dm^3 1.5 dm^3 3.0 dm^3
Hence, 3.0 dm^3 of sulphur trioxide is formed.