When you're stuck on a question, blind guessing is your enemy. Educated guessing, however, is a skill. Since CBSE has no negative marking for Class 10, leaving a question blank is the only way to guarantee zero marks. Here is how to guess intelligently.
In most MCQs, one option is clearly an "outlier." If you have values like 10, 12, 14, and 500, the 500 is likely a distractor. Eliminate it first. Now you've increased your odds from 25% to 33%. Find one more impossible answer, and you're at 50%.
Statistically, in board exams, if "All of the above" is an option and you find at least two options are correct, then "All of the above" is almost certainly the answer.
In Social Science or Biology, options containing extreme words like "Always," "Never," "Only," or "Must" are often incorrect. Scientific and social truths are usually more nuanced, so look for "Often," "Generally," or "Most" instead.
If you forget a formula, check the units in the options. If the question asks for "Work Done" (Joules) and the options are in Watts or Ohms, you can immediately strike them off. Use dimensional logic to narrow down the choices.
In long-form questions, if you don't know the full answer, define the key terms mentioned in the question. You will get step-marks for definitions, diagrams, and formulas even if the final result is wrong.