Question

Multiple of fine structure of spectral lines is due to:
A. presence of main energy levels
B. presence of sub-level
C. presence of electronic configuration
D. is not a characteristics of atom

Answer 1

Hint: When the electron releases energy then spectral lines are formed. Sometimes multiple spectral lines can be seen while doing so. We will discuss the formation of these spectral lines. The reason behind these spectral lines is the release of energy when an electron jumps from higher energy level to lower energy level.

Complete answer:
When we provide energy to an atom, this energy is used by electrons to change its energy level or shell. When the electron jumps from high energy level to lower energy level, then the difference of energy is radiated in the form of electromagnetic radiation. These electromagnetic radiations are called spectral lines. Let us consider an electron jump from fifth energy level to fourth energy level, then the difference of these energy levels is radiated in the form of electromagnetic radiation. But these energy levels contain sub-energy levels also. For example, in the case of the second shell it contains sub-energy levels which are $$2s$$ and $$2p$$, thus these sub-energy levels also take part in radiation. Earlier it was assumed that these sub-level of shells have the same amount of energy and thus the energy difference due to them is zero. But in actuality they all differ by $${10}^{-4}\text{ ev}$$ of energy. Due to this difference, multiple lines of spectra are visible to us.
Hence the correct option is B.

Note:
When electrons jump from higher energy level to lower energy level then it releases energy. When electrons jump from lower energy level to higher energy level then it absorbs energy. Due to the presence of sub-shell of each shell, the multiple lines of spectral can be seen. The difference of energy of the shell is radiated in the form of electromagnetic radiation.