The interval of an octave consists of 12 half steps (or semitones) from a given note. However, if you're referring to the scale degrees, it is often considered as spanning 8 white note names (C to C, for example).
If your question is in terms of pitch intervals, the best answer from your given choices is:
eight.
This refers to the fact that there are eight notes in a diatonic scale when counting the root note to the octave (C, D, E, F, G, A, B, C).