Final answer:
The increase in electronegativity from lithium to fluorine is due to the increase in effective nuclear charge, which results in a smaller atomic radius and thus a greater ability to attract electrons.Correct answer is option C.
Step-by-step explanation:
The electronegativity of the elements increases from lithium to fluorine primarily because of an increase in effective nuclear charge. As we move from left to right across a period in the periodic table, elements have more protons in the nucleus, which increases the nuclear charge. This stronger positive charge pulls the negatively charged electrons closer to the nucleus, thus decreasing the atomic radius.
The atomic radius decreases across a period, which enhances the ability of the nucleus to attract the valence electrons of other atoms during bond formation, resulting in higher electronegativity. Additionally, electronegativity generally decreases from the top to bottom of a group due to the larger atomic size. In the case of Group 17 (the halogens), which includes fluorine, we see the highest electronegativities because they have the most significant ability to attract electrons towards themselves, with fluorine having the highest electronegativity of all elements (EN = 4.0).