// Making the originals as List<string> will be more effecent
List<string> usableItems = new List<string>() { "1", "b7", "13" };
List<string> originalItems = new List<string>() { "1", "3", "5", "b7", "9", "11", "13" };
// Result string Array
string[] discardedItems = originalItems.Except(usableItems).ToArray();
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