Three of the words will be in the same classification, the remaining one will not be. Your answer will be the one word that does NOT belong in the same classification as the others.
Loaf, sourdough, and pumpernickel are types of bread. A rye is not a bread type.
Loaf - Bread that is shaped and baked in one piece and usually sliced before being eaten.
Pumpernickel - Dark, dense German bread made from coarsely ground whole-grain rye.
Sourdough - Leaven for making bread, consisting of fermenting dough, typically that left over from a previous batch.
Rye - A wheatlike cereal plant that tolerates poor soils and low temperatures.
The noun, preposition, and adverb are classes of words that make up a sentence. Punctuation belongs in a sentence, but punctuation is not a class of word.