Answer: The correct answer for the fill in the blank is metallic luster.
Gold is a metal. Thus, it possesses all the properties of metal like ductility, malleability, conduction of heat and electricity, metallic luster.
When the light interact with the surface of gold, it produces brilliant shine. This shine is referred to as its metallic luster.
Gold is opaque and reflective. When light strikes gold surface, it is reflected back and does not pass through gold.
Thus, the correct answer for the fill in the blank is metallic luster.