NDA

These subjects are under the General Ability Test (GAT).
You can get the previous year's papers on Shiksha's link below
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/exams/amp/nda/question-papers&ved=2ahUKEwjQz9LFk-7gAhVLRo8KHdQaBm0QFjADegQIAxAB&usg=AOvVaw03ak-lq0rSN2jqs0O92jEq&cf=1.

I will suggest you to visit the official website as there, they have mentioned the range in which they will allow you for the process.
All the best.

There won't be any problem. To know the teeth condition that can disqualify you are mentioned on this website https://www.ssbcrack.com/2012/10/what-are-14-dental-points.html.

Girls are not eligible for NDA.

I am sharing with you the link of NDA 2019 syllabus for commerce students. If you require any more assistance over the link please let me know. This link is created by Shiksha experts for easy access to students. https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/exams/amp/nda/syllabus&ved=2ahUKEwjNtevVot3gAhVKPo8KHSpjDOMQFjAKegQIARAB&usg=AOvVaw2UCEz9xoi7VsFVM4O5bvwA&cf=1.

Hi Santosh, Please refer to the link below:
https://www.shiksha.com/exams/nda.

You can view the eligibility details here-
https://www.nda.nic.in/eligibilitycriteria.html.

You can buy them from your the nearest book seller and
or you can download them from Shiksha's this link:
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/exams/amp/nda/question-papers&ved=2ahUKEwjNj7e10dLgAhXPfH0KHSrKBwsQFjACegQICRAB&usg=AOvVaw03ak-lq0rSN2jqs0O92jEq&cf=1&cshid=1550951745153
Best of luck.

Well, the NDA written exam has 2 papers. Paper -1 is based fully on mathematics and requires a good knowledge of mathematics of 10th, 11th 12th syllabus. Paper-2 is general ability which includes the GK, physics, chemistry, history. Etc. So it is very difficult for a person who has not studied physics, maths to clear the exam.
Best of luck.

I myself have given the exam of NDA so think I can assist you for this query. Yes, there is a negative marking of -1.33 or you can say 1/3 part of the marks is deducted for each wrong answer. Hope, it cleared your doubt.