Hello,

You need to take admission in NIOS to be eligible to appear in on demand exam.You can give any number of subjects as per your choice and convenience.You can appear in the exam whenever you are ready.Taking maths exam is your choice, it depends on what you want to do after class 12.Say if you want to pursue engineering you need to have mathematics as compulsory subject.So think about all those and take decision.

Please click the link below for more information

https://nios.ac.in/on-demand-examination.aspx#a5