Explain how spectroscopy is used to determine the elements that are present in a star.

Spectroscopy also tells us the age of a star by looking at the amount of its matter made up of chemical elements other than hydrogen and helium. "The earliest stars were composed of just hydrogen and helium because they were the first elements to form after the Big Bang".

Explanation:

the electronic configuration of an atom with eight electrons is 1s²2s²2p⁴. the orbital diagrams are shown in the figure.

as per the hunds rule:

1. electrons tend to avoid being in the same orbital as per as practicable.

2. electrons in different orbitals of the same energy will have their spin parallel.

this can be illustrated from the multiplicity of the orbitals of the atom. as there are four electrons in the p orbital and p orbital has 3 sub-shells. the electrons can be fed in different ways as shown in the figure but the correct orbital diagram will be as per the hunds rule.