context: Together with caesium and gold (both yellow), and osmium (bluish), copper is one of only four elemental metals with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells is such that it corresponds to orange light. The same mechanism accounts for the yellow color of gold and caesium.
question: నింపబడిన 3d మరియు సగం ఖాళీ 4s పరమాణు షెల్స్ మధ్య శక్తి వ్యత్యాసం కాంతి ఏ రంగుకు అనుగుణంగా ఉంటుంది?
answers: orange light