Answer :
Answer:
Explanation:
The correct answer is: principal quantum number.
Here's why:
Principal quantum number (n): This number defines the main energy level of an electron and the distance of the electron's orbital from the nucleus. The rows (periods) of the periodic table directly correspond to the principal quantum number (n) of the outermost electrons in the atoms of the elements. As you move down a group (column), the principal quantum number increases by 1.
Angular momentum quantum number (l): This number defines the shape of the orbital (s, p, d, f). Within a single row (same principal quantum number), elements can have different subshells (s, p, d, f) based on the angular momentum quantum number.
Spin quantum number (ms): This number describes the spin of the electron on its axis (up or down). It doesn't influence the row (period) in the periodic table.
Magnetic quantum number (ml): This number defines the orientation of an orbital within a subshell due to an external magnetic field. It also doesn't affect the row (period) placement.
