Final answer:
The correct answer is 'c) Unordered list', where the order exists without reflecting the properties of the elements, unlike in an ordered list where the elements are arranged based on certain characteristics.
Step-by-step explanation:
When considering the order of elements in a data structure, if there is an order but that order is not based on element characteristics, the correct answer is c) Unordered list. An unordered list simply maintains a sequence of items, but that sequence does not reflect any inherent properties of the items themselves. This contrasts with an ordered list (b), where the arrangement might be based on properties such as numerical value, alphabetical order, or some other form of ranking. A non-empty list (a) signifies that the list contains elements, but does not necessarily indicate anything about the order of those elements. An indexed list (d) implies that each item in the list can be accessed by an index, but again, does not specify how the elements are ordered.