The line spectra of two elements are not identical because-
(A)The element do not have the same number of neutrons
(B)They have different mass numbers
(C)Their outermost electrons are at different energy levels
(D)They have different valencies
The correct answer is (C) Their outermost electrons are at different energy levels.
The line spectra of elements are determined by the energy transitions of electrons within the atoms. When an electron in an atom moves from a higher energy level to a lower energy level, it emits a photon of light with a specific wavelength, creating a line in the spectrum. The exact energy levels that electrons can occupy in an atom are unique to each element.
The energy levels or shells of electrons in an atom are determined by the arrangement of electrons and the number of protons in the nucleus. Elements have different numbers of electrons, and therefore they have different energy levels for electrons in their atoms. This leads to different possible electron energy transitions and different line spectra for each element.
Therefore, the line spectra of two elements will not be identical because their outermost electrons are at different energy levels.