You can purchase a sample book of previous years question paper and practice papers of oswaal or All in one or golden .All the three are equally good. If you are a CBSE student make sure you know everything from the ncrt text book specially for science. Always questions are asked from the text book but they just twist the question to confuse you or add a irrelevant point to test your knowledge. Make sure you know the consepts very well. You can also refer to oswaal or all in one guide for questions and answers .
All the best!