I have got 73% in class 12 board exam 2019 . Am I eligible to seat for Jee advance in 2020.....

Well since you have not mentioned your board i am taking cut off percentile for CBSE as a standard in this question , if you are from a different board you can comment below and i will answer accordingly.

For appearing in jee advance the candidates need to satisfy atleast one of two below mentioned criteria

1)the candidate should have passed 10+2 equivalent  atleast with an aggregate of  75%

2)the candidate should be within the category wise top 20 percentile of successful candidates in their respective 12th standard board examination. Since CBSE's top 20 percentile cutoff is generally 85-86% according to previous years analysis,  you are not eligible to appear for jee advance but if you are serious and dedicated to appear for advance in 2020 then you can always go for improvment, make sure to fill improvement form timely, if you want to appear for improvement in all subjects then top 20 percentile of 2020 will be considered otherwise for few subjects top twenty percentile of  2019 will be considered.

Hiiii NK!!!! Congratulations for your marks first of all. To appear in JEE advance  you need to first of all clear your mains. But for advance you need to have 75% in your 12th if general and rest 65%. so if you are not in general category you can appear. Good luck!!!!