Question

The basic character of $MgO,SrO,{K_2}O$ and $NiO$ increases in the order:
A. ${K_2}O < SrO < MgO < NiO$
B. $NiO < MgO < SrO < {K_2}O$
C. $MgO < NiO < SrO < {K_2}O$
D. ${K_2}O < MgO < NiO < SrO$

Answer 1

Basic character is related to metallic character. Thus, along a period, it decreases from left to right, making alkali metal oxides the most basic. Down a group, it increases due to increase in metallic character.

Complete step by step answer:
Metal oxides react with water to form bases (hydroxides), indicating their basic character. Thus, higher the metallic character of an element, higher will be the basic character of its oxide.
As we move from left to right along a period, the tendency to give away valence electrons decreases, as more number of electrons are being added to the outermost shell. Since metallic character is dependent on an element’s ability to release electrons and form positive ions, we can say that metallic character decreases from left to right along a period. Thus, group one elements (alkali metals) will be the most acidic, and thus, will form the most basic oxides. The next most basic oxides are formed by the group two elements (alkali earth metals).
Also, down a group, since more number of shells are being added, the ability of the nucleus to hold on to its valence electrons decreases, and hence, metallic character increases down a group.
If we look at the elements present in the oxides given, we see that potassium ($K$) belongs to group one, so it will form the most basic oxide. Magnesium ($Mg$) and Strontium ($Sr$) are placed in group two, and thus, they will come next in the series. Among these two, since Strontium is placed more down the group (in period five) than Magnesium (period three), $SrO$ will be more basic. Nickel ($Ni$) belongs to the transition elements and is placed in group ten towards the right of the periodic table. Hence, it will form the least basic oxide.
Therefore, from our observations, the correct order of basicity of the given oxides is:
$NiO < MgO < SrO < {K_2}O$
Hence, the correct option to be marked is B.

Note: The basic character is the exact inverse of acidic character, which is shown by non-metal oxides. Thus, the acidic character of oxides increases as we move from left to right along a period and decreases down a group. Note that in the periodic table, there are elements which display amphoteric oxides, which have properties intermediate between acidic and basic oxides. Also note that metallic character is measured using the ionization energies of elements, which denote the energy required to remove an electron from the valence shell of an atom.