As the period number increases on the periodic table (moving from the top of the table to the bottom), A. the atomic number increases and the atomic mass decreases. B. the atomic number decreases and the atomic mass increases. C. the number of the principal energy level containing the outer electrons increases. D. the number of the principal energy level containing the outer electrons decreases.

The correct option is C. the number of the principal energy level containing the outer electrons increases.

Explanation:

Each chemical element is characterized by the number of protons in its nucleus, which is called the atomic number Z. In the periodic table the elements are placed according to their atomic numbers, in order, in an increasing manner and are represented by the symbol, coming from His name in Latin. You can distinguish horizontal divisions or rows called periods and vertical divisions or columns that are called groups.

The table is divided into periods that are listed from 1 to 7 from top to bottom. Elements that belong to the same period have different properties, but similar masses, because they have the same number of orbitals. That is, the elements that belong to the same period have their electrons arranged in the same number of energy levels. For example, an element with five electronic layers will be located in the fifth period. Then, as the period number increases in the periodic table, the number of the energy level increases, that is, the electronic layer.

Then, the correct option is C. the number of the principal energy level containing the outer electrons increases.

C) the number of the pricipal energy level containing the outer electrons increases