Question

Which element never exhibits a positive oxidation state in any of its compounds?

• A. Oxygen
• B. Chlorine
• C. Fluorine
• D. Carbon

Hint:

Ask which element has no atom above it on the electronegativity scale.

Answer 1

The Correct Option is C

Step 1: The oxidation state of an atom in a bond depends on which atom pulls the shared electrons more strongly, that is, on electronegativity. The more electronegative atom in a bond is assigned the negative oxidation state and the less electronegative partner gets the positive one.
Step 2: Fluorine is the most electronegative element in the entire periodic table, with a Pauling value of about 3.98. Because there is no element more electronegative than fluorine, fluorine can never be forced to give up electron density to a partner atom. In every compound it forms, whether HF, OF₂, or NaF, fluorine keeps a full negative charge on itself, so its oxidation state is always minus 1, and 0 in the free element F₂.
Step 3: Compare with the other elements. Oxygen is highly electronegative but is beaten by fluorine, so in OF₂ oxygen is forced into a rare plus 2 state, meaning oxygen can occasionally show a positive state. Chlorine is less electronegative than oxygen and fluorine, so in oxoacids and oxides such as HClO₄ or Cl₂O₇ chlorine shows positive oxidation states up to plus 7. Carbon is only moderately electronegative and readily shows both negative states (as in CH₄) and positive states (as in CO₂), so it clearly can be positive.
Step 4: Since fluorine has no atom above it in electronegativity to lose electrons to, it is the one element that never shows a positive oxidation state, confirming option C.