2,000-- 3,000 is the rank will get the seat in iit's know. When,10, 000 rank will get iit. And  will not lose iits,,, then 10,00+ rank are going to apply for that

Another doubt
When I qualified for advanced but i don't get seat. What i will do next

Actually what happens is that students who have JEE advance ranks above 5000 do not generally opt for IITs. Because they do npt wish to go for branches like biotech, metallurgy or ceramics. Also, beyond a rank of 5000-6000, you will probably get a newer IIT which is not yet established. That is why you should consider more options as well.Last year,IISC took students who scored 285+ in mains/advance rank within 500.IISER took students within advance rank 7000. I hope you got a rough idea now.Can you please let me know what other options have you kept aside other than IITs?

Looking for chandigarh, srm, manav rachna
Have doubt you haven't answered qualified for advanced but didn't get any seat any opportunities there

IITs have total seats around 10000 but since there are few more new IITs set up this year the total seats have gone up. Additionally, MANY students give up on IITs due to better options available in NITs/IIITs . So, you have a slight chance of getting new IITs even at a rank.of 14000-15000. But I would suggest you to not to give up on some other good colleges(NIT/IIIT/BITS or others) just for the sake of IIT.Also, I would suggest you to choose the branch of your choice instead of going for lower branches in IITs.

Even i qualified for advanced but i don't get seat
Then what i can do

Unfortunately, you cannot do much about it. Advance rankings are released for around 35000 students per year. It is obvious that the last 20000 among these 35000 won't likely get a seat in IITs. So I suggest you to look up for different options that you mentioned and do not stick to getting a seat in IIT.Apart from the IITs, there are many other good colleges that accept the score. To name a few, the following list shows the names of some colleges apart from the ones you mentioned: Indian Institutes of Science Education and Research (IISER): Bhopal, Kolkata, Mohali, Pune, Thiruvananthapuram. Indian Institute of Science, Bangalore. Indian Institute of Space Science and Technology (IIST) Rajiv Gandhi Institute of Petroleum Technology Shiv Nadar University, Uttar Pradesh North Cap University (NCU), Gurgaon Arni University, Himachal Pradesh Alliance College of Engineering and Design