The element with strongest electropositive nature is A ) \[Cu\] B ) \[Cs\] C ) \[Cr\] D ) \[Ba\]
Hint: Electropositivity is the tendency of an atom to donate electrons and form a cation. Metals, such as alkali metals and alkaline earth metals show electropositivity. Electropositivity is just opposite of electronegativity. Consider the properties of groups in which the given elements belong.
Complete answer: In a period, on moving from left to right, the electropositive character decreases and the electronegative character increases. In a group, on moving from top to bottom, the electropositive character increases and the electronegative character decreases. The given elements are copper (\[Cu\]), cesium (\[Cs\]), chromium (\[Cr\]) and barium (Ba). Of the given elements, \[Cs\] and Ba are alkali metal and alkaline earth metal respectively. \[Cr\] and \[Cu\] are transition metals. The properties of transition metals (\[Cr\] and \[Cu\]) are in between the properties of highly electropositive metals (\[Cs\],\[Ba\] etc) and highly electronegative non metals (\[O\], \[S\], \[Cl\]etc.) Hence, \[Cr\] and \[Cu\] cannot be the elements having the strongest electropositive nature. \[Cs\] is alkali metal and Ba is alkaline earth metal. Alkali metals are more electropositive than alkaline earth metals. Alkali metals such as \[Cs\] have only one electron in their valence shell. They can readily lose such an electron and attain electronic configuration of nearest noble gas. On the other hand, alkaline earth metals such as \[Ba\] have two electrons in their valence shell. They can readily lose these two electrons and attain electronic configuration of nearest noble gas. Hence, alkali metals are more electropositive than alkaline earth metals. Hence, the element with the strongest electropositive character is \[Cs\].
So, option B ) is the correct answer.
Note: Electropositive character does not increase with increase in number of valence electrons. It increases down the group and decreases when we are moving left to right in the periodic table.