Dear aspirant,

See, you've not mentioned the name of the Entrance exam for which you are asking about. However the rules and regulations of choice filling and locking are more or less same for all the competitive and Entrance exams.

First of all you can choose any number of choices, even you can choose all of the choices offered to you. Suppose you've selected total of 100 of choices in the Choice filling list and you've sorted them according to your interest from 1 to 100. Now suppose you are being allotted to the institution mentioned in the 45th choice in round 1 of the counseling. Then two things can be happened here. If you become happy with your 45th option or don't want to upgrade it, then you have no choice left other than 45th one. Now coming to the other part, suppose you opt to upgrade for the second round. Then in your list of preferable choices if any of the above 44 choice's seat becomes vacant (i.e. suitable as per your marks and rank) then you become selected for that institution, otherwise the previous 35th number choice becomes your only option. The same thing happens in every round.

However keep one thing in your mind in this regard that under any circumstances you don't have any kind of possibilities to get chance in those receding 55 choices after 45th. So make your list of choices by maintaining proper order so that you don't have to regret for it later.

We all know that choice filling and sorting is very important in any counselling procedure. So please go through the above description minutely.

Now regarding this, I would like to recommend you several Careers360 counselling and choice-filling articles, just have a look:

https://engineering.careers360.com/articles/jee-main-counselling-seat-allotment

https://medicine.careers360.com/articles/neet-counselling

https://engineering.careers360.com/articles/josaa-registration-and-choice-filling

I don't know about which exam you're looking for, that's why I've provided you randomly.

Hope it helps.