In the periodic table, the period number indicates a. the number of dots shown on the lewis dot diagrams for elements in that period. b. the number of valence electrons for elements in that period. c. the reactivity levels for elements in that period. d. the number of the outermost energy level for elements in that period.

B. the number of valence electrons for elements in that period.

This is how the period number indicates the number of valence electrons:

Period      number of valence         elements
                 electrons

1              1                                     Li, Na, K, Rb, Cs, Fr
2              2                                     Be, Mg, Ca, Sr, Ba, Ra
13            3                                     B, Al, Ga, In, Tl, Nh
14            4                                     C, Si, Ge, Sn, Pb, Fl
15            5                                     N, P, As, Sb, Bi, Mc
16            6                                     O, S, Se, Te, Po, Lv
17            7                                     F, Cl, Br, I, At, Ts
18            8                                     He, Ne, Ar, Kr, Xe, Rn, Og

As you see, for the representative groups the last digit of the period number is the number of valence electrons.

Atomicity occurs to prevent updates of the database occurring only partially, which can cause greater problems than rejecting the whole series outright.some are monatomic, diatomic, triatomic etc because it shows the number of atoms. for example, monatomic means it contains only one atom.