Al vs potassium alum

Al and potassium alum both are nouns.

Word	Noun	Adjective	Verb	Adverb
Al	Yes	No	No	No
potassium alum	Yes	No	No	No

As nouns, potassium alum is a hyponym of Al; that is, potassium alum is a word with a more specific, narrower meaning than Al:

Al: a silvery ductile metallic element found primarily in bauxite
potassium alum: a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum

Other hyponyms of Al include alum, potash alum, alum, ammonia alum, ammonium alum.

Al (noun)	potassium alum (noun)
a silvery ductile metallic element found primarily in bauxite	a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum