1. My hobby is internet games and paper folding.

2. My hobbies are internet games and paper folding.
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Which one is grammatical?

3. My hobby is exchanging text messages on Kakao Talk on my smart phone.

4. My hobby is talking with my friends on the phone.

5. My hobby is group chatting.
6. My hobby is chatting in groups on-line.
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Are they all grammatical? Which one is ungrammatical?
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7. My hobby is using the computer.
8. My hobby is to use the computer.
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Can we use both expressions? Which one is commonly used? Do we have to use the ing-form or to infinitive form?

2 answers

Q1) 2 is GRAMMATICALLY CORRECT
Q2) 5 is GRAMMATICALLY CORRECT the rest are NOT GRAMMATICALLY CORRECT
Q3) 8 is the best one. If I were phrasing ANY of these sentences I would do it differently, however 8 is the best choice.
Carpe_Diem is wrong. All except #1 are correct. #1 is wrong because you list two hobbies, not one. The verb should be the plural "are", not "is". Your hobbies ARE (two things), as in #2.