Hello Dipendra, This year JEE Mains was held in two slots (paper 1 and paper 2 respectively) once in January and once in April so that candidates who fail to give their best in the first slot can reattempt in the second and the best of two scores would be taken for ranks determination.

You can check the difference in question paper sets for these different slots here: https://engineering.careers360.com/articles/jee-main-question-paper