Question

The metallic lustre exhibited by sodium is explained by:
A.Diffusion of sodium ions
B.Oscillation of loose electrons
C.Excitation of free protons
D.Existence of body centred cubic lattice

Answer 1

The perception of sight takes place when light is incident on a particular surface of the object. Once this light is incident on this surface, it interacts with the molecules on the surface. A certain portion of energy is absorbed from the incident light and the surface then reflects the remaining light.

Complete step by step answer:
The light which is reflected consists of only certain wavelengths. The remaining wavelengths are absorbed by the surface. Our mind is programmed in such a way that we perceive the wavelength of the reflected light to be the colour of the surface.
In this process, one important energy transfer that takes place is between the surface and the incident light. Light consists of energised particles known as photons. The electronic configuration of sodium is $1{s^2}2{s^2}2{p^6}3{s^1}$ . This means that there is one electron in the valence shell. When photons are incident on the surface of a piece of sodium, they transfer energy to atoms at the surface. This energy causes the excitation of the electrons in the valence shell of the atom and the move to a higher energy state. When the electron returns to its original state, it releases energy that is visible to us in the form of a lustre.
Hence, the metallic lustre exhibited by sodium is explained by oscillation of loose electrons from lower to higher and then again to lower energy states.

Hence, Option B is the correct option.

Note:
This lustre is visible to us only because the energy emitted by the de excitation of the electrons has a wavelength that is perceptible to the human eye. Had the light had lower or higher wavelengths beyond the limit of visible light, we would not have been able to see it.