Oxidizing strength decreases down the halogen group

Steps:

• Identify elements: A is F (Z=9), B is Cl (Z=17), C is Ar (Z=18), D is K (Z=19).
• Recognize halogens (A, B) as strong oxidizers due to ns²np⁵ configuration, seeking one electron for stability.
• Note C (noble gas) and D (alkali metal) lack oxidizing tendency.
• Compare halogens: F > Cl in oxidizing power due to smaller size and higher electronegativity.

Why A is correct:

• Fluorine has the highest electronegativity (4.0 on Pauling scale), giving it the strongest tendency to gain electrons as an oxidizing agent.

Why the others are wrong:

• B: Chlorine is a halogen but has lower oxidizing power than F due to larger atomic size and weaker electron attraction.
• C: Argon is a stable noble gas with full octet, showing no tendency to gain electrons.
• D: Potassium is an alkali metal that readily loses electrons, acting as a reducing agent.

Final answer: A