how to know when we are practice question answer

Dear student,

If you think that you are not able to solve questions, then try to figure out in which part or concept you are lacking.
Because for solving any questions, first you have to revise, the concepts and then try to solve random questions.

Also don't pick up single variety problems, try out multiple problems.

And the best time to solve the questions is - when you complete the syllabus or chapter. Then try to make the mixed problems from all chapters. And just revise only those questions in which you get stuck or made mistake. Also if you think that you are lacking the practice and is not able to solve questions after studying a chapter ( due to lack of practice ), then make the numericals or questions from that chapter or syllabus.