Question

why is fluorine more electronegative than oxygen?
the valence shell is located closer to the nucleus in the oxygen atom than in the fluorine atom.
the oxygen atom is smaller than the fluorine atom causing greater attraction to an electron.
the increased protons and electrons in the same energy level increase the effective nuclear charge.
this is false. oxygen is actually more electronegative than fluorine.

Explanation:

Electronegativity depends on effective nuclear charge and atomic radius. Fluorine has one more proton than oxygen while both have valence electrons in the 2nd energy level. This increases fluorine's effective nuclear charge, pulling electrons more strongly. The other options are incorrect: fluorine's valence shell is closer to the nucleus than oxygen's, fluorine is smaller than oxygen, and fluorine is the most electronegative element (more so than oxygen).

Answer:

The increased protons and electrons in the same energy level increase the effective nuclear charge.