Odd One Out — Iron, Potassium, and Sodium are metals; Chlorine is a non-metal halogen. Select the odd one and explain the grouping.

Introduction / Context:
Chemical classification by metallic character is foundational. Three listed elements are metallic; one is a non-metal.

Given Data / Assumptions:

• Iron (Fe): transition metal.
• Potassium (K): alkali metal.
• Sodium (Na): alkali metal.
• Chlorine (Cl): halogen, non-metal.

Concept / Approach:
Group by metallic vs non-metallic character.

Step-by-Step Solution:
Iron → metal.Potassium → metal.Sodium → metal.Chlorine → non-metal.

Verification / Alternative check:
State under standard conditions: Fe is solid metal; K and Na are soft reactive metals; Cl2 is a greenish gas—another differentiator.

Why Other Options Are Wrong:

• Iron, Potassium, Sodium: all metals; they form cations in compounds.

Common Pitfalls:
Confusing high reactivity (K, Na) with “not metal”; reactivity does not negate metallic character.

Final Answer:
Chlorine