For performing less no of search operations out of a large elements, which searching technique is good enough such that the elements are not sorted?

If the elements aren't sorted, then you can't do a binary search. But binary search is so much faster than linear search (you'd need to look at an average of 10 elements rather than 500) that you'd be best sorting your list (using an algorithm such as quicksort) and then doing a binary search.

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