Hey.

The cut off for the previous year of Tamil Nadu NTSE was 127 marks out of 150 in 2018 and 120 marks in 2018. You can expect a similar range this year. The cut off may vary year to year according to various factors like level of exam, no of candidates etc. The maximum marks this year is also 200  unlike previous year. So you seem to have feweer chances to qualify if you score 150 if a similar cut off trend is seen this year too.
Rest depends on the factors this year.
Best of luck!

https://www.google.co.in/amp/s/school.careers360.com/articles/ntse-tamil-nadu-cutoff/amp