Hello,

NTA JEE Main 2021 will be held in 4 sessions - February, March, April, and May. Paper-I will be conducted in all four sessions but Paper (2A & 2B) will be held in February and May sessions only. To compute the All India Rank in the JEE Main exam, the best of the four NTA JEE Main 2021 scores will be taken.

Yes you can appear for all the four sessions of JEE Mains provided that you have applied for them.

For february if you haven't applied then you can not appear for it. For the other three sessions the registration window will be open fr a short duration in the respective month

Good Luck