1. Most of the apples are rotten/bad.
2. Most of the water was polluted.
3. Two-thirds of the chestnuts were spoiled.
4. Two-thirds of the milk was contaminated.
(Are all the expressions grammatical?)
Yes, all are fine. In the first sentence, either word will work fine.
Yes, all of the expressions provided are grammatically correct. However, there are slight differences in the usage of certain words.
1. Most of the apples are rotten/bad.
Both "rotten" and "bad" are valid adjectives to describe the condition of the apples. You can use either of them depending on your preference or the context in which you are using the sentence.
2. Most of the water was polluted.
Here, "polluted" is the correct adjective to describe the state of the water. It means that the water has been contaminated or made unclean in some way.
3. Two-thirds of the chestnuts were spoiled.
"Spoiled" is the correct adjective to describe the state of the chestnuts. It means that the chestnuts have gone bad or become unfit for consumption.
4. Two-thirds of the milk was contaminated.
"Contaminated" is the correct adjective to describe the state of the milk. It implies that the milk has been mixed with impurities or harmful substances.
In summary, all of the expressions provided are grammatically correct. However, the choice of adjectives may differ depending on the specific circumstances or context in which they are used.