My blog is around 1 year old and have PR2. The average daily pageviews upto last 1 week were 1800. The total number of posts are 180.

Though I have only 180 total posts, the total number of Indexed URL was increasing and it was as high as 510. But in the month of Sept2012, the total number of Indexed pages dropped from 510 to 214. The drop was sudden and it is now increasing very slowly.

Also, the other main concern is huge increase in 'Not Selected' number. It is currently 814. I have never posted any post again and never copied any idea from any other blog. But I do use internal linking to some older post those are related to the new posts.

The questions are:;

1. Why there is sudden drop in the 'Total Indexed' pages.
2. Why there was increase in total indexed pages to 500 even though the total posts were only 180.
3. As the drop in 'Total Indexed' was in the month of sept2012, I was getting same organic traffic and it was steadily increasing till last week and then there was a 50 drop in the total pageviews. Why.
4. Now, again the traffic is becoming to normal but still there is a problem.
5. Is increase in the 'Not selected' number is a cause of drop in 'Total Indexed'?
6. How to prevent or reduce the number of 'Not Selected' even though I do not have any duplicate post withing blog.
7. Is the 'internal linking' to older post creating 'Not selected' problem?
8. Should I edit my 'Robot.txt' to avoid crawling of labes that may be creating duplicate posts or something like that, if so, what is correct robot.txt.

I have uploaded the screenshot of the graph of Webmaster Tools. Please take a look and give suggestions.

Please help. Thank you in advance.