Answer:
The answer.
Explanation:
Group 17 consists of Halogens, and group 18 consists of Noble Gases.
Group 17 are very high electronegativities. They have seven valence electrons. They are highly reactive, especially with alkali metals and alkaline earth.
In group 18 their elements are the most stable due to having the maximum number of valence electrons their outer shell can hold. Therefore, they rarely react with other elements since they are already stable.
Nobel gases are placed there because they are extremely unreactive.
Halogen elements are placed there because they have seven valence electrons, they only require one additional electron to form a full octet.
