Final answer:
The element's principal quantum number is most easily identified by looking at the period number of the element on the periodic table. The period corresponds to the principal quantum number, which indicates the electron shell occupied by the electrons of an element.
Step-by-step explanation:
To identify an element's principal quantum number easily, you can look at b) the period number of the element on the periodic table. Each row on the periodic table is termed a 'period' and it corresponds to the principal quantum number (n). The principal quantum number is a number that specifies the electron shell that an electron occupies in an atom. For example, elements in period 1 have a principal quantum number of 1, elements in period 2 have a principal quantum number of 2, and so on. The periodic table is organized in such a manner that the atomic number increases from left to right and from top to bottom, indicating the number of protons and, indirectly, the electron configuration as well. When you examine the periodic table, you will find that the atomic number (number of protons) appears above the element's symbol, and the atomic mass appears below. The mass number, however, is different from the principal quantum number and is not directly related to it, as the mass number is the sum of protons and neutrons in the nucleus and does not easily reveal information about electron configurations. The position of an element on the periodic table can also be used to deduce its atomic number, atomic mass, and other physical and chemical properties, but for the principal quantum number specifically, the period number is what you need to know.