The inner core, although composed almost entirely of pure iron, is thought to contain traces of lighter elements, primarily oxygen and silicon. (discovermagazine.com)
These results provide an experiment - based mass — radius relationship for a hypothetical pure iron planet that can be used to evaluate plausible compositional space for large, rocky exoplanets. (nature.com)
The hydrogen peroxide provides this since vinegar isn't a strong enough oxidant to make more iron oxide from pure iron. (wellnessmama.com)