Final answer:
The group number of a representative element mainly indicates the number of valence electrons in the highest occupied energy level.
Step-by-step explanation:
From knowing the group number of a representative element on the periodic table, you can determine the number of electrons it has in the highest occupied energy level. This is because the group number (for groups 1-2 and 13-18) usually corresponds to the number of valence electrons, which are the electrons in the outermost energy level. For example, the elements in Group 1 are known as alkali metals and have one electron in their outermost energy level, while Group 17 elements are halogens and have seven valence electrons. However, this does not provide information about the number of filled energy levels, protons and neutrons in the nucleus, or the total number of electrons. Those details require additional information such as the period number and the atomic number.