chlorine dioxide vs whitener

chlorine dioxide and whitener both are nouns.

Word	Noun	Adjective	Verb	Adverb
chlorine dioxide	Yes	No	No	No
whitener	Yes	No	No	No

As nouns, whitener is a hypernym of chlorine dioxide; that is, whitener is a word with a broader meaning than chlorine dioxide:

chlorine dioxide: an explosive gas (ClO2) used chiefly in bleaching paper or starch or soap or flour and in water purification
whitener: an agent that makes things white or colorless

Other hypernyms of chlorine dioxide include blanching agent, bleach, bleaching agent, dioxide.

chlorine dioxide (noun)	whitener (noun)
an explosive gas (ClO2) used chiefly in bleaching paper or starch or soap or flour and in water purification	an agent that makes things white or colorless