Q.What do the principal quantum number 'n' and azimuthal quantum number 'l' of an electron belonging to an atom represent?
Which principle is followed in the distribution of electrons in an atom?

The periodic table's row-and-column structure is a direct, mechanistic consequence of how electrons fill orbitals. The period number of an element equals the principal quantum number n of its valence (outermost) shell — period 1 has 2 elements because the first shell holds at most 2 electrons, period 2 and 3 each have 8 elements as the second/third shells' s and p subshells fill, and periods 4-7 have 18 or 32 elements as inner d and f subshells are filled in between. Down any group, elements are expected to share the same general outer electronic configuration, since a new outer shell is simply added at each step (this holds cleanly for groups 1, 2 and 13-18; groups 4-12 only s …