What is the best way to revise an entire subject in two days before a CBSE exam?

With two days, do not reread everything; revise strategically. First, look at the blueprint and previous years' papers to see which chapters carry the most marks, and start there. Use your own notes, formula sheets and chapter summaries rather than the full textbook, because they trigger recall faster. Do active recall: close the book and try to write the key points, then check what you forgot, and re-revise only the gaps. Solve at least one full previous year paper or sample paper within the time limit to find weak spots. The night before, lightly skim definitions, diagrams and formulae rather than learning new things, and sleep properly. Trying to cover every line in two days leads to remembering nothing clearly, so prioritise high-weight, high-confidence content.