Why is a spectrum for a given element unique for that element?

A. No element has more than two electrons in the first shell.

B. Each element has a unique arrangement of electrons.

C. Atoms of different elements have different masses.

D. Atomic nuclei contain no electrons.

The answer is d. i just took the test

Answer: B. Each element has a unique arrangement of electrons.

Explanation:

1) Since the number of electrons in neutral atoms is equal to the number of protons, and the number of protons are unique for each element, each element has a unique arrangement of electrons.

2) The spectrum of an element is the radiation emitted for the atoms of the element when the valence electrons are emitted and that depended on the electrons configuration.