Which example illustrates the phonological process of deaffrication?

Deaffrication is a phonological process where an affricate sound, which combines a stop and a fricative, is replaced by a fricative sound. In English, the affricate /tʃ/ (as in "chew") can undergo deaffrication.

In the example provided, "chew" pronounced as /ʃu/ shows the substitution of the affricate sound /tʃ/ with the fricative /ʃ/. This accurately illustrates deaffrication because the articulatory action changes from the complex consonant sound of an affricate to a simpler, single fricative sound.

The other examples represent different phonological processes. The pronunciation of "round" as /waʋnd/ shows a change to a glide, "dog" pronounced as /dɔd/ reflects a process of final consonant deletion or consonant harmony, and "van" pronounced as /fæn/ demonstrates voicing assimilation rather than deaffrication. Thus, the choice that exemplifies deaffrication is indeed the correct one.