CBSE Class 12-science Answered

It depends on the question which you are solving. If you are solving a question which involves solving an equation, then you can definitely substitute the solution back and check. However, this does not mean that you can check the answers for all your questions. Most of the time, you will not be able to check the answers for problems on mensuration, geomtry, statistics, vectors etc. In calculus also, you can differentiate/integrate the solution to arrive back at the problem. 

Sometimes, some questions can be solved by 2 different ways and you might want to do that in the end (when you have time) just to ensure that you are getting the same solution from both the methods.