Hello,

I will give you the clarification. You have got 51 Score in chemistry and it is equivalent to your percentile in chemistry, it's your sectional percentile or NTA score, not your overall percentile. You must have scored different percentiles in Physics and Maths, on the basis of your overall NTA score, you can find your overall percentile, to find your predicted percentile please go through this link

after getting your predicted percentile, you can find your predicted rank by clicking on the same aforementioned link.

To know more about Marks vs Percentile, visit this link

https://engineering.careers360.com/articles/jee-main-marks-vs-percentile/amp

Good Luck.