Question

Valency of the elements in the halogen group is _______.
(A) one
(B) two
(C) three
(D) four

Answer 1

Hint:Halogens belong to group $17$ of the periodic table, consisting of highly reactive elements including fluorine, chlorine, bromine etc. General electronic configuration of halogens is $n{s^2}n{p^5}$ that is they have seven electrons in their outermost shell.

Complete step by step answer:
In halogens, there are seven electrons in the outermost shell i.e.$ns^2 np^5$ as per the electronic configuration and they are short of one electron to achieve the nearest noble gas configuration. So, to achieve their nearest noble gas configuration they have great tendency to accept an electron, and so they are highly electronegative and thus they accept an electron exhibiting an oxidation state $\left( { - 1} \right)$ and form stable compounds. Thus the valency of the elements in the halogen group is one.
So, the correct option is $\left( A \right)$, as they are short of only one electron for completing their octet.

Additional Information:-
Halogen are highly reactive non-metallic elements in the group $17$ of the periodic table. Halogens including Chlorine, fluorine etc often combine with alkali metals in group $1$ commonly sodium (Na) of the periodic table to form salts, as alkali metals have just one electron in their outermost shell, which they are equally eager to donate. Thus these highly reactive non- metals react with metals to form salts.
Halogens are existing in a variety of colors and are the only periodic table group consisting of elements in all the three states of matter, namely solid, liquid or gas. Chlorine is a gas, bromine is a liquid while iodine is a solid.


Note:
Halogens are non metals and require one electron to achieve noble gas configuration, and so their valency is one as they gain one electron. On the other hand, metals have only one electron in their outermost shell so they donate it to achieve their noble gas configuration and so their valency is also one, as they lose one electron. Reactions involving halogens can be highly explosive especially near the top of the group as they are highly reactive in nature due to strong tendency to gain one electron and form stable compounds.