Hello, I have a question...If I write one article and submit it in 2 days to 500 or more article directories. then Is it Spam? Is it going to increase my rank for keyword?
That alone will not increase you rank for a keyword. Optimize your page/website and get some quality backlinks from trusted sites also - besides articles submission
If it was this easy then everyone would be doing it. The search engine would be trashed with bunch of duplicates.
google itself has duplicate content filter and will filter out the duplicate pages by either not indexing them or removing form indexing. so if you submit same article to 500 sites, you will more than like get only few backlinks unless you spin the article to generate atleast 30%+ unique versions. other search engines however are not much into duplicate content filtering yet so you will get the backlinks on yahoo and MSN but i suggest you spin the article for originality. there are content spinners available and you can chk to see if you find any good ones.