Taxon represents taxonomic group of any rank. Each plant belongs to a hierarchy of taxa which are assigned taxonomic ranks. For example, different taxa for onion are Allium cepa (species rank), Allium (genus rank), liliaceae (family rank), thus Allium cepa, Allium, liliaceae are different taxa to which onion belongs.
Name of a species refers to group of potentially interbreeding, morphologically similar individuals. A genus is a taxonomic rank that constitutes single species of monophyletic group of species that share a sum total of characters, though they cannot interbreed. A group of closely related genera, that share some common morphological features but are reproductively incompatible, constitutes a family. Thus, names of species, genus and family represent taxa of a particular hierarchy which makes them wrong answer as a taxon can belong to any of taxonomic ranks.
Therefore, the correct answer is option D.