Question

Lithium, sodium and potassium belong to the same group called alkali metals. Why?

Answer 1

Hint: The alkali metals are the first group of elements in the periodic table. Because they are extremely reactive, they are found in nature bound with other atoms. Lithium, sodium, potassium, rubidium, caesium, and francium are alkali metals.

Complete answer:
Because lithium, sodium, and potassium all have the same valence electron, that is one, they are all members of the same group. Because all of these elements create oxides, which dissolve in water to form alkali, the group is known as alkali metals.
A metal whose hydroxide is a water-soluble base is referred to as an alkali metal. The term "earth" refers to an element's oxide mineral. An alkaline earth metal is one whose oxide has characteristics comparable to those of an alkali.
 If a metal oxide possesses alkali qualities, the metal's hydroxide should also have alkali properties. Alkali metals react with oxygen in the air and with regular oxides to form alkali metals. When heated in air, all elements in the group first produce conventional oxides, while all metals in other groups, with the exception of lithium, form peroxide. All metals, with the exception of lithium and sodium, produce superoxides.

Note:
Because they are in the same group, alkali metals have comparable chemical properties but differing reactivity. This implies that their outermost shells will have the same number of valence electrons.