Hello,
According to your question the answer of these question is like that:-
In the modern periodic table, the period indicates the value of, principal quantum number (n) for the outermost shell or the valence shell.
Hope you understand it!!

Hello dear!

Arrangement of the elements. The horizontal rows of the periodic table are called periods.
In the modern periodic table, the period indicates the value of,principal quantum number (n) for the outermost shell or the valence shell.

Hope you like my answer.

Hello dear!

I hope so that you are doing well and you are safe.

So in the modern periodic table the period indicates the value of,

1.principal quantum number (n) for the outermost shell or the valence shell.

2.Atomic number

3.Atomic mass      4.Azimuthal quatam number.

Best of for your journey.