1. If you give me a piece of rice cake, then I will not eat you.

2. If you give me a rice cake, then I will not eat you.

3. If you give me some rice cake, then I will not eat you.

4. If you give me some rice cakes, then I will not eat you.

5. If you give me rice cake, then I will not eat you.

(Which expressions are grammatical?)

1- 4 are okay.

5 would not be used.

To determine which expressions are grammatical, we can analyze the subject-verb agreement and the correct use of articles.

1. If you give me a piece of rice cake, then I will not eat you. (grammatical): This expression is grammatically correct, as it uses the singular article "a" before the singular noun "piece" and the singular noun "rice cake."

2. If you give me a rice cake, then I will not eat you. (grammatical): This expression is also grammatically correct. It uses the singular noun "rice cake" without an article, which assumes a general or unspecified rice cake, and the subject-verb agreement is maintained.

3. If you give me some rice cake, then I will not eat you. (grammatical): This expression is grammatically correct. It uses the plural noun "some rice cake," which indicates an indefinite quantity, appropriately matching the subject-verb agreement.

4. If you give me some rice cakes, then I will not eat you. (grammatical): This expression is also grammatically correct. It uses the plural noun "some rice cakes," indicating multiple rice cakes, and the subject-verb agreement is maintained.

5. If you give me rice cake, then I will not eat you. (not grammatical): This expression is not grammatically correct because it lacks an article or a determiner before the noun "rice cake." To make it grammatical, you would need to use an article like "a" or "some," such as "If you give me a rice cake" or "If you give me some rice cake."

In conclusion, expressions 1, 2, 3, and 4 are all grammatically correct, whereas expression 5 is not grammatically correct.