hi,

nios board exam is offline mode, however to obtain a pass certificate candidates need to choose atleast of 5 subjects,need to choose  1 or maximum of 2 subjects from group A, and other 3 subjects from another group, however candidates are free to take any two subject as optional, however taking optional subject is not mandatory.

you may follow the below link to know about group wise subjects list,

https://nios.ac.in/departmentsunits/academic/senior-secondary-course-equivalent-to-class-xii.aspx