Final answer:
The density of the purple gas is 0.5 g/ml.
Step-by-step explanation:
The density of a substance is calculated by dividing the mass of the substance by its volume. In this case, the mass of the purple gas is 10g and the volume is 20ml. To find the density, divide the mass by the volume:
Density = Mass/Volume = 10g/20ml = 0.5 g/ml
Therefore, the density of the purple gas is 0.5 g/ml.