Despite DL's not accepting ít, "the three states of water" is the normal English.
At least you can drop the second "the"
From Chinese 狀態
Why not ‘the three states’?
Don't ask me.
The 3 states of the water
THE three states of water is correct English. Please change this.
You have no hope of that. Dulingo arbitrarily throws in a 'the' or takes it without regard to standard English. I think it's because it's written by Vietnamese speakers whose understanding of the nuances of English is elementary and limited.
Countries have states. Water does not. So I would translate nước here as "country"
Liquid, solid, gas, not Kansas, Nebraska, Michigan.