Question

The decreasing order of basic character of ${{K}_{2}}O$, BaO, CaO and MgO is _________.
(A) ${{K}_{2}}O$ > BaO > CaO > MgO
(B) ${{K}_{2}}O$ > CaO > BaO > MgO
(C) MgO > BaO > CaO > ${{K}_{2}}O$
(D) MgO > CaO > BaO > ${{K}_{2}}O$

Answer 1

The basicity of oxides has relation with the electropositivity of the metal involved in the oxide. We can say that the more electropositive the metal, more basic its oxide will be and vice versa.

Complete step by step answer:
Here, we are asked about the order of the basicity of the given oxides.
- We can see that all the oxides given here are metal oxides. We know that all the oxides and all metals are generally basic.
- We can say that the reason for the variation in basicity of oxides is the metal atom. More electropositive the metal atom, the more basic oxides it will form. So, we can say that oxides of more electropositive metals will be more basic and vice versa.
- We are given ${{K}_{2}}O$ , MgO, CaO and BaO to compare their basicity. They involve K, Mg, Ca and Ba metals.
- We know that in periodic tables, as we go downwards in groups, the electropositivity of the element increases. As the atomic number increases in a period of periodic table, the electropositivity of an element decreases.
- Out of all these metals only K (Potassium) is situated at group-1 of the periodic table. So, it will have the highest electropositivity amongst Ca, Ba, K and Mg. So, its oxide ${{K}_{2}}O$ will be the most basic oxide from a given group of oxides.
- Then, Ca, Ba and Mg are all alkaline earth metals and they are situated in group-2 of the periodic table. So, we know that as we go down in the groups, the electropositivity increases. So, Mg is in first period, Ca is in second period and Ba is in third period of the periodic table. So, Order of electropositivity of these metals will be Ba > Ca > Mg. Thus, the order of basicity of their oxides will also be the same. So, BaO > CaO > MgO.
Thus, we can finalize their basicity order as ${{K}_{2}}O$ > BaO > CaO > MgO
So, the correct answer is “Option A”.

Note: Do not forget that K and alkaline earth metals are not situated in the same group. Remember that more electropositive metal forms more basic oxides and less electropositive metals forms less basic oxides.