Final answer:
The correct statement is that the word 'keychains' contains 3 morphemes and at least 6 phonemes, as it is composed of the morphemes 'key', 'chain', and the plural suffix '-s'.
Step-by-step explanation:
The student's question pertains to the linguistic concepts of phonemes and morphemes, which are fundamental units of sound and meaning in language, respectively. Statement 2) is incorrect because elephants contains more than one morpheme: the root elephant and the plural suffix -s. Statement 1) is therefore also incorrect as it describes an inaccurate number of phonemes and morphemes for the word elephants. Statement 3) is accurate as the word keychains consists of three morphemes: key, chain, and the plural suffix -s. The word keychains contains more than three phonemes, thus making statement 4) incorrect.
Correct statement: 3) The word keychains contains 3 morphemes and 6 phonemes.