Note: 2.5 10^3 kg = 2.5 10^3 10^3 = 2.5 10 ^6 g, Because 1 kg = 10^3 g
This is simple proportion
1.80 grams of air has a volume of 1 liter.
1 gram of air would have a volume of (1/1.8) liter
Therefore, 2.5 10^6 g would have: 2.510^6 (1/1.8) = 1.3888 10^6 liters of air.