What functional chord symbol is used to denote the tonic note of a minor key?

In music theory, particularly in the context of minor keys, the tonic chord is crucial as it establishes the tonal center of the piece. The functional chord symbol that is used to denote the tonic note of a minor key is represented in lowercase, which indicates a minor quality. Therefore, the symbol "i" signifies the tonic triad built on the first scale degree of the minor scale, reflecting its minor tonality.

In contrast, the uppercase symbols like "I," "IV," and "V" typically represent major chords, which are not appropriate for identifying the tonic in a minor key. Thus, the symbol "i" directly communicates the nature of the tonic in minor keys, based on the scale degrees that define their structure and character. This is fundamental knowledge in understanding chord functions within different tonalities.