Hey after 12th class if you want to join Indian army NDA exam is the best option .

I am here suggest you best books for Preparation for NDA examinations.

Books :

Pathfinder for NDA & NA Entrance Examination Conducted by UPSC (English) 7th Edition (Paperback)
Rs. 595
Author: Experts Compilation
Publisher: Arihant


NDA & NA Chapterwise - Sectionwise Solved Papers : Mathematics / English / General Ability with Explanatory Solutions (English) 5th Edition (Paperback)
Rs. 295
Publisher: Arihant


Handbook of Chemistry A Multipurpose Quick Revision Resource (English) (Class - 11th and 12th)
Rs. 299
Author: Arihant Experts
Publisher: Arihant Publications(I) Pvt.Ltd – Meerut


NDA & NA National Defence Academy and Naval Academy Entrance Examination: 10 Practice Sets (English) 1st Edition (Paperback)
Rs. 230
Author: Expert Compilations
Publisher: Arihant Publications(I) Pvt.Ltd – Meerut


NDA/ NA 10 years Topicwise Solved Papers (2006-2015) 3rd Edition (English) (Paperback)
Rs. 378
Publisher: Disha Publication


NDA/NA Previous Solved Papers (English) 1st Edition (Paperback)
Author: Gupta, R
Publisher: Ramesh Publishing House