Question

The most electropositive element among the following is:

• A. Na
• B. Ca
• C. K
• D. Cs

Hint:

Electropositive character increases as you go down a group.

Answer 1

The Correct Option is D

Electropositive character simply means how easily an atom gives away an electron to become a cation. The key factor is the distance of the outermost electron from the nucleus.

• Going down a group, each new period adds another electron shell, pushing the valence electron farther from the nucleus and increasing shielding by inner electrons.
• Farther and more shielded means the nucleus holds that electron more weakly, so the atom gives it up more easily, that is, electropositivity rises down a group.
• Among Na, K and Cs, all Group 1, Cs sits at the bottom of the group with the largest size and the most shells, so its valence electron is easiest to remove.
• Ca is a Group 2 element and, despite being reactive, holds on to its electrons more strongly than the alkali metals because it has a higher nuclear charge for a comparable period.

Comparing all four, caesium loses its outer electron most readily, so option D is correct.