Hii

As such, there is no such criteria in NEET exam. The paper can be set from anywhere in the syllabus. The syllabus as mentioned by NTA is the complete topics covered in class 11th and 12th So you will have to cover up each and every part of the syllabus to score good marks.
Its just that some topics are given more importance while others are less important but nothing like only 16 topics are asked.
For example only 2% weightage is given to chapters physical world and units and measurement in Physics class 11th while thermodynamics has 9% weightage.
Optics from class 12th has 10% weightage while atoms and Nuclei has only 3% weightage.
Basic concepts of chemistry class 11 has only 1% weightage while thermodynamics has 8% weightage. 9% weightage is given to coordinate compounds while chemistry in everyday life has only 2% weightage.
In biology, Human physiology has 20% weightage while structural organisation has only 5% weightage in class 11th syllabus and for class 12th syllabus, Genetics and evolution has 18% weightage but only 4% weightage is gvien to biotechnology and its applications.

So basically every chapter is important, its just that a number of questions out of the total are from some particular parts but there is minimum 1 or 2 questions from every chapter.
Here is a link which you can use to get the complete chapterwise weightage of all the syllabus for NEET - https://medicine.careers360.com/articles/neet-chapter-wise-weightage-and-important-topics
Also you can checkout our NEET knockout package which is available for online studies. It willprovide video lectures, test series, doubt clearance and a lot of study material for your NEET preparations. Here is the link - https://www.entrance360.com/knockout-neet-may/?utm_source=C360&utm_medium=qna&utm_campaign=knockout-neet-may
Also check the NEET Rank booster which has the most frequently asked topics, and important questions - https://www.entrance360.com/neet-rank-booster/?utm_source=C360&utm_medium=qna&utm_campaign=neet-rank-booster

Hope this helps
Thanks!!