Question

which of the following statements about valence electrons ar the periodic table is true?
a the number of valence electrons decreases from left to right across each period.
b elements with the most valence electrons are in group 18.
c all of the elements in group 9 have nine valence electrons.
d the number of valence electrons increases from top to bottom within each group.

Explanation:

• Option a: The number of valence electrons increases from left to right across each period (not decreases). For example, in period 2, lithium (\(Li\)) has 1 valence electron, beryllium (\(Be\)) has 2, and so on until neon (\(Ne\)) with 8.
• Option b: Group 18 (noble gases) elements have a full valence shell. Helium (\(He\)) has 2 valence electrons, and other noble gases (e.g., neon (\(Ne\)), argon (\(Ar\))) have 8 valence electrons. Since the maximum number of valence electrons for main - group elements (excluding some transition - metal cases which are more complex) is 8, elements in group 18 have the most valence electrons among main - group elements.
• Option c: The maximum number of valence electrons for an atom (in the context of the simple valence - electron counting for main - group - like behavior, ignoring some complex transition - metal electron - counting rules) is 8. So, no element has 9 valence electrons.
• Option d: The number of valence electrons is the same within each group. For example, all elements in group 1 (alkali metals) have 1 valence electron, and all elements in group 2 (alkaline earth metals) have 2 valence electrons.

Answer:

B. Elements with the most valence electrons are in group 18.