Hey,
Yes, there is a possibility to take only mathematics subject from Nios. NIOS provides various general and academic courses at secondary and senior secondary level. They offers candidate to choose any one or two of three different languages. So register as a NIOS senior secondary student and fill the form for on demand paper of math on NIOS website. They will allow you to add a maths subject . You write only the Maths subject and write it.
Hope this helps.
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