Question

which of the following oxides is most acidic in nature?
A) $MgO$
B) $BeO$
C) $CaO$
D) $BaO$

Answer 1

As we know that acidic nature is decided by the lower value of ionisation energy and higher value of electron affinity or electron gain enthalpy. And down the group ionisation enthalpy and the electron gain enthalpy decreases due to increase in the size of an atom.

Complete solution:
As we know that the ionisation energy which is the amount of energy which should be supplied to an atom to remove an electron from an isolated gaseous atom to form a gaseous cation. It decreases down the group because the size increases which decreases the attraction of valence electrons and the nucleus and thus a small amount of energy is required to remove that valence shell electron.
The lower value of ionisation energy results in the greater metallic character and thus greater basic character of the element as well as greater will be the electropositive character while moving down the group.
Similarly, when the amount of energy released in addition of an electron to an isolated gaseous atom to form gaseous cation is the electron gain enthalpy and when the element has the higher value of electron affinity, it results in the greater acidic character and non-metallic nature.
So, from the above explanation we can say that while moving down the group the acidic nature decreases and therefore, Beryllium oxide ($BeO$) will be most acidic in nature and Barium oxide is least acidic in nature.
Therefore, from the above explanation we can say that the correct answer is (B).

Note: Remember that on moving down the group, the metallic character of the elements increases and thus the basic character will increase on moving down and thus the element on top will be highly acidic and along the period the acidic nature increases on moving from left to right in case of metals and in case of non-metals on moving from left to right in the period the acidic nature decreases.