A problem solving rule of procedure that when followed step by step, assures that a correct solution will be found is known as :

The answer is C) Algorithm. An algorithm is a systematic, step-by-step procedure that, if followed correctly, is guaranteed to reach a correct solution. Following a recipe or the long division method are everyday examples. The question is really testing a precise definition, and the key word is 'assures'.

• A) Mental set is a tendency to approach a problem with a strategy that worked earlier, which can block a better solution. It is a hindrance, not a procedure.
• B) Trial and error is a heuristic where you try options and learn from failures. It offers no guarantee of success and can take very long.
• D) Insight is the sudden restructuring of a problem that makes the solution appear, as in Kohler's chimpanzee experiments. It is not a step-by-step rule.

Core concept: problem solving in cognitive psychology, where algorithms are contrasted with heuristics. Algorithms are exhaustive and reliable but can be costly in time; heuristics are quicker shortcuts but fallible. This connects to Mains decision-making and administrative problem solving in the ethics and governance papers.

Trap: candidates pick 'Trial and error' because it also involves steps. The decisive word is 'assures'. Trial and error does not guarantee a correct solution, whereas an algorithm does.