The V7 chord of C major is the G dominant 7th chord, written as G7. In the key of C major, the V chord is built on the fifth note of the C major scale, which is G. The dominant 7th chord is formed by taking the root (G), major third (B), perfect fifth (D), and minor seventh (F) of the G major scale.

To illustrate this, let's take a look at the G major scale: G A B C D E F# G

To form a dominant 7th chord, we take the root (G), major third (B), perfect fifth (D), and minor seventh (F) from the G major scale: G B D F

Combining these notes, we get the G7 chord: G B D F

In the context of C major, the G7 chord is often used to create tension and resolve back to the tonic chord (C major). This is because the dominant 7th chord has a strong tendency to resolve to the tonic chord due to the dissonance created by the minor seventh interval.

Here are a few examples of the G7 chord in the key of C major:

1. In a basic chord progression: C - G7 - C This progression uses the G7 chord as a dominant chord leading back to the tonic chord (C).

2. In a blues progression: C7 - F7 - G7 In blues music, the dominant 7th chords are commonly used. In this example, the G7 chord serves as the V7 chord in the key of C major.

References:

• https://www.musictheory.net/lessons/43
• https://www.guitar-chords.org.uk/chords-key-c-major.html