Question 25

Rubidium is an alkali metal.

Rubidium is classified as an alkali metal because it belongs to Group 1 of the periodic table, which contains elements that readily lose their outermost electron to form positive ions.

A) magnesium

Magnesium is not an alkali metal; it is an alkaline earth metal found in Group 2 of the periodic table. Alkaline earth metals have two valence electrons, unlike alkali metals, which have one.

B) rubidium

Rubidium is indeed an alkali metal, characterized by its single valence electron in its outer shell. This property allows rubidium to react vigorously with water and form strong bases, typical of alkali metals.

C) hydrogen

Although hydrogen is located at the top of Group 1, it is not considered an alkali metal in the traditional sense. Hydrogen has unique properties that set it apart from alkali metals and does not exhibit the same reactivity and behavior as they do.

D) chlorine

Chlorine is a halogen and is found in Group 17 of the periodic table. It has seven valence electrons and typically gains an electron to form negative ions, which is contrary to the behavior of alkali metals.

Conclusion

Rubidium is the only correct answer as it is classified as an alkali metal, exhibiting the defining characteristics of this group. Other options, including magnesium, hydrogen, and chlorine, either belong to different groups or do not share the same properties associated with alkali metals. This distinction is crucial for understanding the behavior and reactivity of elements in the periodic table.