What interval does the 2nd harmonic create above the octave?

The interval created by the 2nd harmonic above the octave is a perfect fifth. When considering the harmonic series, the fundamental frequency (1st harmonic) serves as the reference or starting note. The 2nd harmonic is an octave above the fundamental, and the 3rd harmonic, which follows, gives us a perfect fifth above the 2nd harmonic.

To clarify, if we take a fundamental pitch (let's say a C note), the 1st harmonic would be that C itself, the 2nd harmonic would be the C one octave higher, and the 3rd harmonic would then be a G, which is a perfect fifth above the C that is an octave above the fundamental pitch. Thus, the interval formed between the 2nd harmonic and the 3rd harmonic is what we refer to as a perfect fifth. This relationship explains why the correct option reflects the interval between these harmonics accurately.