Hello,

• IIT/NIT admission through JOSAA and CSAB requires Class 12 from a recognized board approved by the Association of Indian Universities (AIU).
• Where as BOSSE (Sikkim) is a recognized state board, so it is generally valid.
• NWAC is an international board, but it is accepted only if you have an equivalence certificate from AIU.

So, BOSSE is valid. For NWAC, you need to confirm equivalence with AIU before applying.

Hope this clear your doubt!