Question

Which of the following statements is not true for halogens ?

• A. All form monobasic oxyacids.
• B. All but fluorine show positive oxidation states.
• C. All are oxidizing agents.
• D. Chlorine has the highest electron-gain enthalpy.

Answer 1

The Correct Option is B

To determine which statement is not true for halogens, let's evaluate each option:

1. All form monobasic oxyacids: This is true. Halogens, except fluorine, can form oxyacids like HClO, HBrO, etc.
2. All but fluorine show positive oxidation states: This statement is incorrect. The halogens can exhibit positive oxidation states except for fluorine, which only shows a -1 oxidation state because it is the most electronegative element and does not have empty d-orbitals to allow higher oxidation states.
3. All are oxidizing agents: This is true. Halogens are good oxidizing agents due to their high electronegativity and ability to gain electrons.
4. Chlorine has the highest electron-gain enthalpy: This is incorrect. Although chlorine does have a high electron-gain enthalpy, it isn’t the highest. Fluorine has a slightly lower electron-gain enthalpy due to repulsion in the small-sized F⁻ ion but is often considered higher in reactivity, leading to common misconceptions.

Thus, the statement "All but fluorine show positive oxidation states" is incorrect regarding fluorine, which does not exhibit positive oxidation states.