mentally retarded vs developmentally challenged

mentally retarded and developmentally challenged both are nouns.

Word	Noun	Adjective	Verb	Adverb
mentally retarded	Yes	No	No	No
developmentally challenged	Yes	No	No	No

As nouns, mentally retarded and developmentally challenged are synonyms defined as:

mentally retarded and developmentally challenged: people collectively who are mentally retarded

Other synonyms of mentally retarded include retarded.

mentally retarded (noun)	developmentally challenged (noun)
people collectively who are mentally retarded	people collectively who are mentally retarded