Hello Saurabh,

Since you have not mentioned any exam in particular is difficult to say for sure. Generally , there can only be two possibilities . One is if you do not fill the choices and lock it, the authority will randomly allot a seat based on you marks or rank or whatever it that is considered for selection along with other details like category or quota etc.  Another possibility is that they will reject your application or won't allot a seat during the counselling process. You may directly contact the authority in case you need any assistance on this issue.

All the best