Why is the pauli exclusion principal an important key into understanding the periodic table

The pauli exclusion principle is a generalized fundamental of energy relationships between electrons within the same atom.  according to the pauli exclusion principle, electrons in atoms form shells and give atoms their chemical properties which depend  on the number of electrons in the outermost shell, which gives rise to the method in which the  periodic table is sorted.

Gallium melts near room temperature and has one of the largest  liquid  ranges of any metal, so it has found use in high temperature thermometers.

It dont even matter because at the end of thre day we gone life like it ius s