Which scale consists solely of five notes?

The pentatonic scale is recognized for consisting solely of five distinct pitches. This scale is widely utilized in various musical traditions across the world, including folk, pop, and even some classical music. The term "penta" refers to five, which directly indicates the scale's structure.

In contrast, other scales mentioned involve either more or different structural elements. The diminished scale, for example, consists of eight notes and is built using alternating whole and half steps, creating a different sound profile and complexity. The natural scale, more commonly referred to as the major or minor scale, features seven notes per octave, making it a seven-note scale. The scale of thirds also implies a specific construction that features intervals of thirds, typically leading to a pattern that exceeds five notes.

Thus, the pentatonic scale stands out clearly as the only five-note scale among the choices provided.