The line spectrum of two elements is not identical because:(A) They do not have the same number of neutrons(B) They have dissimilar mass number(C) They have different energy level schemes(D) They have different number of valence electrons

The line spectrum of an element is produced when electrons in atoms move between discrete energy levels, emitting light at specific wavelengths corresponding to the energy difference between these levels. Each element has its unique set of energy levels, determined by its atomic structure.
• Option A: The number of neutrons does not affect the energy levels of an atom because neutrons do not participate directly in the electron transitions responsible for emission spectra. Therefore, the line spectrum is not influenced by the number of neutrons.
• Option B: The mass number (which is the sum of protons and neutrons) also does not directly affect the electron energy levels. Isotopes of the same element (with different mass numbers) have identical electron configurations, and therefore, identical line spectra.
• Option C: The line spectrum of elements differs because each element has a unique arrangement of electrons and energy levels. These unique energy level schemes lead to different wavelengths of light being emitted when electrons transition between levels.
• Option D: The number of valence electrons can influence the chemical properties of an element, but the line spectrum is primarily determined by the electron transitions between energy levels, not by the number of valence electrons.
Final Answer:
C) They have different energy level schemes