Hello student,
Yes NIOS is a recognized board if you qualify on demand Mathematics examination from NIOS board yes you're eligible to appear in Jee main.
Eligibility - Candidates must passed or appearing class 12 in Physics chemistry and Mathematics with minimum 75 percent marks aggregate from a recognized board.
For more details refer to the link mentioned below - https://www.google.com/url?sa=t&source=web&rct=j&url=https://engineering.careers360.com/exams/jee-main&ved=2ahUKEwjF_9uY0eTrAhVN7nMBHUPQDVIQFjAAegQIChAC&usg=AOvVaw1k3rMyr-Osb0qy4gsPfOaR
Feel free to comment if you've any doubt
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