Question

An element $A$ combines with oxygen to form an oxide $AO$ . The oxide is electrically conducting. Find the number of valence electrons in $A$ .
A.$1$
B.$2$
C.$3$
D.$4$

Answer 1

In this first we need to know the electronic configuration of oxygen. From this we will get to know the number of valence electrons oxygen has. Then we will get to know the valence electrons of $A$ in oxide $AO$ .

Complete step by step answer:
-Electronic configuration is defined as the number of electrons that are distributed in the orbitals of an element.
-Electronic configuration of oxygen $\left( O \right) = 1{s^2}2{s^2}2{p^4}$ .
-Therefore, to complete its octet state it requires only $2$ electrons in its outermost shell to get completely filled.
-So for this, first we need to find valence electrons of element $A$ .
-Valence electrons: it is defined as the number of electrons that are required by the outermost shell of an atom to completely fill its shell or number of electrons required by the outermost shell to fill completely.
-Since, oxygen requires $2$ electrons in its outermost shell, these $2$ electrons are known as valence electrons.
-Therefore, valence electrons of oxygen are $2$ .
-When this oxygen combines with an element $A$ it forms an oxide $AO$ .
-This means that $1$ atom of element $A$ reacted with $1$ atom of oxygen.
-Therefore, the valence electrons of an element $A$ will be the same as that of the oxygen.
-Thus, the valence electron for element $A$ will be $2$ as that of oxygen.
So, the correct answer for this will be option b) $2$.

Note:
Valence electrons give us an idea on how the atoms can bond and take part in bonding. It also helps us to determine the chemical properties of an element. It can also absorb or release energy in the form of photons.