Differnt positions on the case of "preposition + relative pronoun"

1. The level of the gas density has been growing, the reason for which is unspecified.
2. The level of the gas density has been growing, for which the reason is unspecified.

3. The level of the gas density has been growing, which the reason for is unspecified.

4. The level of the gas density has been growing, which the reason is unspecified for.

5. She always asked me about the issue, my opinion on which wasn't clear.

6. She always asked me about the issue, on which my opinion wasn't clear.

7. She always asked me about the issue, which my opinion on wasn't clear.

8. She always asked me about the issue, which my opinion wasn't clear on.

9. She always asked me about the issue, my opinion about which would be quite worthless.

10. She always asked me about the issue, about which my opinion would be quite worthless.

11. She always asked me about the issue, which my opinion about would be quite worthless.

12. She always asked me about the issue, which my opinion would be quite worthless about.

Q) Which sentences are correct English or grammatically acceptable?

I think that except 12, all the sentences seem to be grammatically acceptable and correct English, although some of them sound a little unnatural.