Which reason best explains why metals are shiny?

Metals are shinny BECAUSE THEIR VALENCE ELECTRONS OSCILLATE BETWEEN BANDS.

Metals generally are shinny in nature, because they possess large number of free, delocalized electrons, which move between different bands in the metal crystals. These free electrons produce a cloud of negatively charged electrons on the surface and underneath the smooth surface of the metals and make them to have shinny appearance.

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.