1. どうして? is more polite expression than なんで. どうして=How about _? なんで=why? 2. きけんな is adjective+verb, and あぶないis adjective. きけんな=hazardous あぶない=dangerous 3. ちがい=difference ちがう=differ だめ=done for,Tha's it.

危険(な) is a Sino loanword. It's more literary. あぶない is a Japanese native word, so it sounds more colloquial and less formal. We use the latter more in daily conversation.

Hi rjcorraya, I'm going to try. 1. What are the main differences between なんで and　どうして? They means the same. なぜ、どうして、なんで　(formal→informal) We don't generally say なんで？ to our boss, for example. 2. Also, main differences between きけんな　and あぶない? They also means the same, but I think きけんな is more danger than あぶない. In canversation we say ”あぶない!!!" when there is something danger, we don't say "きけん!!! " 3. What are the correct usages of ちがい / ちがう and　だめ? ちがいis noun, ちがう is adjective ちがう means "be different", so we use it when someone makes a mistake (for example). だめ is noun (sorry, I'm not sure!), だめな is adjective. We use it, for exaple, there is something prohibited. (informal) 食べてはだめ。TVを見てはだめ。 Hope it helps you and you get more answers!