Hi Aditya, 

Only students studying in class 10 are eligible to appear for NTSE exam. You can apply for other scholarship exams, such as KVPY and Olympiad exam. 

Hey.

No, NTSE Examination is not for students of Class 12th. This exam is conducted by NCERT only for students from Class 10th. 

You can use the link below to download the Information brochure for NTSE for any more details.

http://www.ncert.nic.in/programmes/talent_exam/index_talent.html

Best of luck!