UGC NET Questions (Paper – 1)

This option is correct because one of the fundamental axioms of probability states that the total probability of all outcomes in a sample space is 1. When outcomes are mutually exclusive and exhaustive, exactly one of them must occur. Therefore, adding their probabilities must give 1. This ensures that some outcome always happens.

Option A:
A total probability of 0 would mean that no outcome can occur, which contradicts the idea of running an experiment. Probabilities must be non-negative and at least one outcome must have positive probability. Thus, the sum cannot be 0 for an actual experiment.

Option B:
The value 1 represents certainty that some outcome from the sample space will occur. Since mutually exclusive and exhaustive outcomes cover all possibilities without overlap, their probabilities must add up to 1. This matches the basic probability axiom, making this option correct.

Option C:
A sum of 1/2 would imply that there is only a 50% chance that any outcome in the declared space occurs. That would mean half the probability lies outside the listed outcomes, so the set would not be exhaustive. Hence, this value cannot be correct here.

Option D:
The value 100 without the percent sign does not fit the standard probability scale from 0 to 1. Even if interpreted as a percentage, it would correspond to 1 on the probability scale, but the question expects the probability value, not the percentage number. Therefore, 100 is not the right answer.