Final answer:
Affricates cannot serve as the nucleus of a syllable because they combine both a stop and a fricative, making them incompatible with the sonorant and continuant properties required for a syllable nucleus.
Step-by-step explanation:
Affricates cannot be the nucleus of a syllable because they involve both a stop and a fricative. Syllable nuclei typically require sonorant sounds which can be sustained and allow the airflow to resonate continuously, resulting in a pitch that can vary in duration and intensity. Affricates, being a combination of a stop (where airflow is completely stopped) followed by a fricative (where airflow is partially obstructed), do not possess these characteristics of a sonorant. The nature of affricates makes them suitable for the onset or coda of a syllable but not the nucleus. They do not lack voicing, as affricates can be either voiced or voiceless, and their duration is not inherently too short but simply unsuitable for use as a vowel or syllabic consonant.