The given part of the modern periodic table is period 2.

The electropositive character decreases as the atomic number increases while moving left to right in a period. 

In Lithium the valence electron is attracted by 3 protons of its nucleus while in other elements of this period the number of protons attracting the valence electrons is higher than 3. 

Thus, it is easier to remove a valence electron from other elements than Lithium. Electro positivity refers to the tendency of an element to lose electrons and form positive ions. 

Hence, Lithium is the most electropositive.