I can fail to get 75% in board exams in 2019,then I fill improvement of all 5 subjects in 2020 but I can only give 1 exam. so, their is any possibility so that I can take 75% in board exams. please tell me.
The only possibility is when you work hard on it. You need to study well for the improvement exam if you don't get 75% in class 12% as per your wish. If you are allowed to take only one subject for improvement, take a subject in which you can do well and get more marks, the subject you find easy compared to others. Study well. Solve previous year question papers. This will help you gain good marks.
Hope this helps.
Good luck!