my d.o.b is 28 dec 2005 how many chances will i get for nda exams if i am now in 10 class ?

There is no cap on the number of limits to be eligible for NDA. As long as your age is between 16.5 years to 19.5 years you are eligible to sit for NDA. Now you are in class 10. To be eligible for NDA, you have to complete 10+2 for Army Wing and 10+2 with Physics and Mathematics for Air Force and Naval Wings. The candidates who are going to appear for final exam can also apply for NDA. There is no such barrier in number of attempts as long as you fulfill the eligibility criteria. You can check this here http://competition.careers360.com/articles/nda-eligibility-criteria You have enough time to prepare for NDA. So start your preparation from now. NDA Syllabus consists of Mathematics part and General Ability Test. The Mathematics part contains topics like Set, Relations, Functions, Calculus, Trigonometry, Geometry, Complex Numbers, Conic Sections, Applications of Integral, Quadratic Equations and Inequalities, Permutation and Combination, Logarithm, Matrices, Determinants, Probability, Vector Algebra etc. The GAT part contains- English Grammar and Vocabulary, Geography, history, economics, Politics, Chemistry, Physics, Biology, Current Affairs, Statistics etc. You can download previous few years question papers http://competition.careers360.com/articles/nda-question-papers