Final answer:
The primary characteristic of the voiced alveolar or postalveolar approximant is it is a liquid sound.
Step-by-step explanation:
The primary characteristic of the voiced alveolar or postalveolar approximant is it is a liquid sound. A liquid sound is a term used in phonetics to refer to sounds that have a smooth, non-turbulent airflow. Alveolar consonants are consonant sounds that are produced with the tongue close to or touching the ridge behind the teeth on the roof of the mouth. The name comes from alveoli - the sockets of the teeth. The consonant sounds /t/, /n/ and /d/ are all alveolar consonants. This sound is not a fricative, plosive, or nasal sound. In the case of English, an example of this sound is the consonant represented by the letter 'r' as heard in words like 'red' and 'car'. The voiced alveolar or postalveolar approximant is represented by the IPA symbol /ɹ/ and is often referred to as the English /r/ sound.