I think I saw on Sun website that there are total of 51 questions and you need to get 35 correct answers to pass the SCJA but some threads here where people share their exam experiences said that there are 122 questions.
No, no, no! There are not 122 questions! Don't worry.
51 sounds about right.
Before Sun releases an exam, they do a beta run, and ask people to come in and do a test exam. Those beta exams usually throw over a hundred questions at the users, and from the results, the decide which questions they want to keep, improve, or throw away. So, if you read about an exam with 122 questions, it must have been someone relating their experience about doing a beta exam. The beta went away years and years ago. If you write the SCJA exam today, you'll see somewhere around 51 questions.