Question

elements in the same group have the same...
a. valence shell
c. energy level of outer electrons
b. number of valence electrons
d. period

Explanation:

In the periodic table, elements in the same group (vertical column) have the same number of valence electrons. Valence electrons are the electrons in the outermost shell of an atom and are responsible for the chemical properties of an element. For example, all elements in Group 1 (alkali metals) have 1 valence electron.

• Option a: The valence shell (energy level of the outermost electrons) is different for elements in the same group as we move down the group (e.g., in Group 1, hydrogen has valence shell \(n = 1\), lithium has \(n=2\), sodium has \(n = 3\) etc.).
• Option c: The energy level of outer electrons (related to the principal quantum number \(n\) of the valence shell) increases as we move down a group.
• Option d: Elements in the same period (horizontal row) are in the same period, not the same group.

Answer:

B. number of valence electrons