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

The question asks which statement is not true for halogens, and the correct statement is, "All but fluorine show positive oxidation states."

1. All form monobasic oxyacids.
   • Halogens like chlorine, bromine, and iodine form monobasic oxyacids such as hypochlorous acid (HOCl), hypobromous acid (HOBr), and hypoiodous acid (HOI).
   • These acids contain one ionizable hydrogen (hence, monobasic).
2. All but fluorine show positive oxidation states.
   • This statement is not true because fluorine always exhibits a -1 oxidation state due to its high electronegativity and does not show positive oxidation states.
   • Other halogens (Cl, Br, I) can exhibit positive oxidation states in their compounds, e.g., Cl in HClO₄.
3. All are oxidizing agents.
   • Halogens are known to be strong oxidizing agents. They can receive electrons from other elements or compounds, thereby oxidizing them.
4. Chlorine has the highest electron-gain enthalpy.
   • This is true as chlorine is highly electronegative, and it has a high tendency to gain an electron, making its electron-gain enthalpy the highest among the halogens.

In conclusion, among the given options, the statement "All but fluorine show positive oxidation states." is not true as fluorine does not show positive oxidation states.