Metals are lustrous because of

Explanation

As we know that metals have a tendency to lose electrons, the outermost electrons are loosely bound and easily break away from metal atoms. These electrons can freely move about the surface of metal and are therefore called mobile electrons. Because of these mobile electrons, light falling on the surface of a metal is not transmitted but is reflected, and hence the metals appear lustrous.
Alternative explanation: A metal’s outer band of mobile electrons will mostly reflect light.