Question

The less electropositive element is:
A. Na
B. Be
C. Li
D. Mg

Answer 1

Hint: Electropositivity increases with increasing metallic character. The more easily an element will donate its electron, more will be its electropositivity. Electropositivity decreases across the period and increases down the group.

Complete answer:
Electronegativity is the relative tendency of a bonded atom to attract a shared electron pair toward itself. Electronegativity is unitless and does not depend upon electronic configuration. On moving down the group with increase in atomic size, electronegativity decreases. Along the period with increasing effective nuclear charge, electronegativity increases.
Higher oxidation state of an element has higher electronegativity than lower oxidation state of the same element. Electronegativity is directly proportional to percentage s character. Electronegativity of an element is not a constant value and electronegativity of inert gas is considered zero due to their stable configuration. Higher electronegativity generally corresponds to higher non metallic character.
Electropositivity is just opposite to electronegativity. An element with higher electronegativity is less electropositive and vice versa. Higher electropositivity corresponds to higher metallic character. On moving down the group with increasing metallic character, electropositive character increases. On moving along the period, with increasing electronegativity or increasing non metallic character, the electropositivity decreases.
As in our question, given elements are lithium, sodium, beryllium and magnesium. Lithium and sodium belongs to group 1 or alkali metals and belongs to period 2 and 3 respectively. On the other hand, beryllium and magnesium belong to group 2 or alkaline earth metal and belong to period 2 and 3 respectively. As electronegativity decreases or electropositive increases on moving down the group, means period 3 elements are more electropositive than period 2 elements. On moving along the period, electronegativity increases or electropositive decreases, means group 1 is more electropositive than group 2. The order for electropositive for these elements will be: sodium>lithium>magnesium>beryllium.

Thus, the correct option is B.

Note: Electronegativity scales are Pauling scale and Mullikan scale. Pauling scale is based upon bond energy and Mullikan scale explains electronegativity as average of ionization energy and electron affinity. Caesium is the most electropositive element. Fluorine is the most electronegative element in the periodic table.