2. To all intents and purposes = Correct
3. For all intensive purposes = WRONG! You should have paid attention in English class!
de jure: Taken literally, the phrase means "for purposes which are intense. All purposes which are not intense are not included." This is almost completely opposite to what is meant by most people, and is why it is imperitive that persons use the proper phrase.
She was a young ditzy female who as her day job taught math and as her night job did modern dance. EXACTLY the type of person you would expect to say "For all intensive purposes."