problem #$21($a$-$b$)$ Briefly explain what determines the characteristic color of $($a$)$ a metal and $($b$)$ a transparent nonmetal. $($c$)$ Sketch and compare the light$-$solid interaction $($transmission$,$ absorption$,$ and reflection$)$ intensities as a function of wavelength in $($a$)$ and $($b$)$ cases, explain the differences