Which interval listed is dissonant?

• A. Unison
• B. Perfect Fifth
• C. Tritone
• D. Major Third

Answer: (C)

Dissonance arises from how two pitches interact: some interval pairings create tension that naturally wants to move to a more stable sound. The tritone, spanning six semitones (an augmented fourth or diminished fifth), sits right between the octave’s stable extremes and introduces noticeable beating and a sense of unsettledness in most tonal settings. That tension is what makes it dissonant. By contrast, unison is just the same pitch and sounds perfectly stable; a perfect fifth has a simple, strong harmonic relationship and feels very stable; a major third also sounds fairly smooth and consonant. So the interval that is dissonant is the tritone.