Question

Which of the following elements will have most electropositivity?
(A) Mg
(B) Na
(C) K
(D) Ca

Answer 1

Hint: Electropositivity is the tendency of any element to lose electrons and form a cation. In a periodic table from left to right the electropositive character decreases, while from top to bottom the electropositive character increases. It is the property of metals.

Complete step by step answer:
-First of all we will see what electropositive character is.
Electropositive character is the tendency of any element to lose electrons and form positive ions known as cations. It can also be known as metallic character because metals have the tendency to lose electrons and form cations while the non-metals have the tendency to gain electrons and form anions. More is the electropositive character of any metal, more easily it will lose electrons and hence lower will be its ionisation enthalpy. So, we can conclude that metals with higher electropositive character will easily lose electrons and are more metallic in nature.
-The alkali metals are most electropositive in nature.
-We will now talk about the periodicity in the periodic table related to electropositivity.
Along a period (from left to right) in a periodic table the tendency of the elements to lose electrons decreases and hence from left to right the electropositive and the metallic character decreases. This is so because when we move from left to right the shell number remains the same but the number of electrons in it increases, which increases the effective nuclear charge. With increase in charge it becomes difficult for an atom to lose an electron and hence its electropositivity decreases. Along a group (from top to bottom) in a periodic table the tendency of the elements to lose electrons increases and so from top to bottom the electropositive and the metallic character increases. This is so because as we move from top to bottom the outer shell number increases with each period and so the distance of the outermost electron from the nucleus increases. With increasing distance the force with which the nucleus attracts the outermost electron will decrease and makes it easy for the atom to lose its outermost electron and form a cation. So, from top to bottom the electropositivity increases.
-Also we should know that the electropositivity of the group 1 elements (alkali metals) is more than the group 2 elements (alkali earth metals). This is so because the general configuration of group 2 is $n{s^2}$ while that of group 1 is $n{s^1}$. Here for group 2 the s-subshell is completely filled and more stable than for group 1 and so it will be more difficult to remove an electron from a fulfilled s-orbital than a half filled s-orbital. Hence group 1 loses electrons easily as compared to group 2 elements.
-We will look at the options to see which of them has the highest electropositivity.
For (A) Mg: It is an alkali earth metal, belonging to the 2nd group and 3rd period. It loses 2 electrons and forms $M{g^{ + 2}}$ ion.
For (B) Na: It is an alkali metal, belonging to the 1st group and 3rd period. It loses an electron and forms $N{a^ + }$ ion.
For (C) K: It is an alkali metal, belonging to the 1st group and 4th period. It loses an electron and forms ${K^ + }$ ion.
For (D) Ca: It is an alkali earth metal, belonging to the 2nd group and 4th period. It loses 2 electrons to form $C{a^{ + 2}}$ ion.
Since we already know that alkali metals have the highest electropositivity and from top to bottom the electropositive character increases, so the element having highest electropositivity is: Potassium (K).

Hence the correct option will be: (C) K

Note: The metals have the tendency to lose electrons and hence are electropositive in nature. But the non-metals have the tendency to gain electrons and hence are electronegative in nature. In a periodic table from left to right the tendency of the elements to gain an electron increases and so the electronegative character increases. From top to bottom the tendency of an element to gain an electron decreases and so electronegative character also decreases.