Answer:
The mass of half a liter of water is 500g, that is, 0.5kg.
Step-by-step explanation:
Density is mass divided by the volume, that is:

Here, we have to be careful. Since the density is in grams per cm³, m has to be in grams and v in cm³.
We have that:

What is the mass of half a liter of water?
One liter is 1000 cm³.
So half a liter is 1000/2 = 500 cm³, which means that 
Then



The mass of half a liter of water is 500g, that is, 0.5kg.