Question

Which of the following elements (atomic number given in brackets) have valency $2$?

• A. $\mathrm{C}\left(6\right)$
• B. $\mathrm{P}\left(15\right)$
• C. $\mathrm{Mg}\left(12\right)$
• D. $\mathrm{Ar}\left(18\right)$

Answer 1

The correct option is C

$\mathrm{Mg}\left(12\right)$

The correct option is (C).

Explanation of Correct Option:

1. Valency is the ability of an atom to gain or lose electron in order to achieve the noble gas configuration.
2. Valency $2$ means $+2$ or $-2$, there can be gain/loss of $2$ electrons from the outermost shell in the atom.
3. The valency of an element is equal to the number of valence electrons or equal to the number of electrons required to complete eight electrons in valence shell, whichever is lower.
4. The atomic number of Magnesium$\left(\mathrm{Mg}\right)$ is $12$. Thus, it's electronic configuration is $(2,8,2)$.
5. Thus, it's valency is $2$.

Explanation of Incorrect Options:

Option (A) :

1. The atomic number of Carbon$\left(\mathrm{C}\right)$ is $6$. Thus, it's electronic configuration is $(2,4)$.
2. Thus, it's valency is $4$.

Option (B):

1. The atomic number of Phosphorus$\left(\mathrm{P}\right)$ is $15$. Thus, it's electronic configuration is $(2,8,5)$.
2. Thus, it's valency is $3$.

Option (D):

1. The atomic number of Argon$\left(\mathrm{Ar}\right)$ is $18$. Thus, it's electronic configuration is $(2,8,8)$.
2. Thus, it's valency is $0$.

Hence, Magnesium $\left(\mathrm{Mg}\right)$ has valency $2$.