Hi Akanksha,

Questions relating to Assertion Reasoning are an important part of AIIMS Syllabus and generally very tricky. However, if we look at a pattern of the  past-years, it seems that most of the questions are produced from NCERT itself. Therefore, firstly be really thorough with NCERT. Look for more conceptual questions rather than explanatory ones. 

Also, there is no one book which has it all in it. These questions are about practicing a wide  variety of questions. However, you can look at the following books:

1. Assertion and Reason for competitive exams by MTG publication. 

2. AIIMS Assertion & Reason (Second Edition: 2017) Paperback – 2017 by Ajay Dogra (Author)

3. Assertion and Reasoning by Arihant Publication. 

Keep updated and keep reading Careers 360 using the link given below: https://www.careers360.com/question-how-to-solve-the-assertion-and-reasoning-questions-in-aiims

Thanks,