A dominant seventh chord (D7) consists of the notes D, F#, A, and C. In the key of D# major (Des dur), the D7 chord would be the V7 (dominant seventh) chord, resolving to the tonic chord of D# major (Des dur). In the key of B minor (b moll), the D7 chord would be the dominant seventh chord, resolving to the tonic chord of B minor (b moll). In the key of B major (h dur), the D7 chord would also be the dominant seventh chord, resolving to the tonic chord of B major (h dur). In the key of G# minor (gis moll), the D7 chord would be the dominant seventh chord, resolving to the tonic chord of G# minor (gis moll). Each resolution creates a sense of tension and release, adding to the harmonic progression and overall musical structure.