C#

The modern chakra-tone correspondence system pairs seven chakras against the seven natural notes of the diatonic scale, C, D, E, F, G, A and B, and was never extended by its original twentieth century Theosophical authors to the five chromatic notes, C sharp among them, that fall between those seven. This is a structural gap rather than an oversight anyone tried and failed to close: a seven note correspondence and a twelve note chromatic scale simply do not divide evenly, and closing the gap would require either doubling some chakras onto two notes or inventing additional correspondences with no basis in either the original chakra literature or the original note-pairing scheme.

Later popular writers have occasionally proposed chakra assignments for the chromatic notes, sometimes reaching for subtler or transitional states between the two neighbouring natural-note chakras, but these proposals are individual inventions rather than an agreed extension of the system, and different authors' proposals for C sharp do not agree with one another. The honest position is that C sharp sits outside the correspondence system as usually stated, not that it has a hidden or disputed chakra waiting to be settled.

C sharp and D flat name the same pitch under the twelve-tone equal temperament tuning used in virtually all modern Western instruments, a relationship called enharmonic equivalence: the piano key that sounds this pitch is a single key regardless of which name a piece of written music gives it. Which name a composer or performer uses is generally decided by the key signature and the harmonic context of the passage rather than by any property of the pitch itself, since a note functioning as the raised third degree of a chord is more naturally read and written as one name and the same pitch functioning as the lowered second degree of a different chord is more naturally read as the other.

Before equal temperament became standard, older tuning systems such as meantone temperament did not treat C sharp and D flat as identical in pitch at all, tuning them very slightly apart; the now-familiar idea that every enharmonic pair sounds exactly the same is itself a consequence of the specific tuning compromise equal temperament represents, adopted across most of Western music only over the seventeenth through nineteenth centuries.