This present book has been specially published for aspirants of Indian Navy-sailors (SSR) , National defence academy (NDA) , Airforce , and combined defence services (CDS) recruitment exams. The book comprise , along with latest study material, basic concepts for better understanding, which will be proven extremely useful for readers to be well conversant with exam pattern , the type of questions asked and their answer. The concept will be also helpfull for board exams .