Is g natural and f natural a semitone?

Yes, G natural and F natural are a semitone apart. In Western Music Theory, a semitone is the smallest interval between two pitches, and it occurs between adjacent keys on a piano keyboard. Specifically, moving from F to G (or vice versa) involves passing through F# or G♭, which makes the distance a whole tone rather than a semitone. Thus, G natural and F natural are indeed a whole tone apart.