Which of the following is an alveolar sound?

An alveolar sound is produced when the tongue makes contact with the alveolar ridge, which is the bony ridge located just behind the upper front teeth. The sound 'Z' is classified as an alveolar sound because it is articulated by placing the tongue against the alveolar ridge. This placement allows the air to flow over the tongue, producing the characteristic voiced sound associated with 'Z'.

In contrast, the other options represent different places of articulation. 'K' is a velar sound, articulated with the back of the tongue against the soft palate. 'P' is a bilabial sound, produced by bringing both lips together while releasing air. 'M' is also a bilabial sound, similar to 'P' but voiced, where the vocal cords vibrate as air escapes through the nasal cavity. Understanding these differentiations helps in identifying various phonetic classifications within speech sound development.