more then 500 less then 600

Basically, there is no such rule that your article must contain so-so words. Besides of this, your article should be informative which can help others. Your article should be unique. It should be written by doing some original research on that subject. Also you should not spin articles cause that's nothing but spamming and would be triggered by Google.

Think back 20 years, if you're old enough. How many items did you encounter that you could read in a given day? One newspaper? Maybe a magazine a few times month? Perhaps you read books, but probably no more than one at a time. Maybe you listened to the radio. Or watched TV. How many cable channels did your service deliver then? Think back before cable (if you can). How many TV channels did you have to choose from then? Five? Ten, if you lived in a big city?

Now, think about today. Maybe the number of print newspapers you read is down. (Sigh.) But how many websites do you see on a given day now? What about Facebook and Twitter? How many links come across your computer or phone each day? Do you listen to podcasts? What about satellite radio? Digital TV? Do read e-books? How many more options do you have to read or listen (or play) in a given day, compared with 10 years ago? Or 20? Or 30?

Unless you own the website, an article index would require customers to publish content that has 400-500 conditions, with appropriate structure, and right submission of keywords.

Generally, there is no such guideline that your content must contain so-so terms. Besides of this, your content should be useful which can help others. Your content should be exclusive. It should be published by doing some exclusive analysis on that topic. Also you should not whirl content cause that's nothing but new spamming and would be activated by The search engines.

Unless you own the blog site, an article directory would require users to submit content that has 400-500 words, with proper format, and right distribution of search terms.