Asian Sciences Olympiad 2015 — Division M, Level 3 (Years 7–9) Question 24

The mass of a 250 ml conical flask is 128.30 grams. A vacuum pump is used to remove the air from the flask. The mass of the evacuated flaskis now measured to be 128.00 grams. (1 m³= 1000 litres).
The best estimate of the density of air is: