Dinesh, the difficulty of obtaining 100 percentile in JEE MAINS PAPER 2 is quite relative and depends largely on your preparation and most importantly the analysis of past few years question papers. Now, let us take the case of January JEE PAPER 2, there were 112679 candidates participating in the exam, some of them who were giving the exam just to test their aptitude but most of them gave the exam with at least few months of preparation and if you want to obtain 100 percentile, then you have to get marks more than all of them, be it "not-so- serious ones" or the ones who have devoted all the time for this attempt, which does make the task a bit difficult. However, you should believe in yourself and concentrate on your preparation rather than what others are doing and believe in the simple fact that someone would get 100 percentile in the merit list, so why can't it be you?