Question

Which of the following sets of elements is not correctly arranged according to the given property?

• A. \( S>Se>O \) (Electron gain enthalpy)
• B. \( F>O>Cl \) (Electronegativity)
• C. \( Na>Li>Al \) (Metallic radius)
• D. \( Na>K>Ba \) (Metallic nature)

Hint:

Remember, metallic nature increases as you move down a group and decreases across a period.

Answer 1

The Correct Option is D

Step 1: Understanding Periodic Trends 1. Electron Gain Enthalpy: The correct trend follows \( S>Se>O \), as oxygen has a lower electron gain enthalpy due to its small size and electron repulsion. 2. Electronegativity: Fluorine has the highest electronegativity, followed by oxygen and chlorine, making \( F>O>Cl \) a correct order. 3. Metallic Radius: Across a period, metallic radius decreases, while down a group, it increases. The given order \( Na>Li>Al \) is incorrect since aluminum is a metalloid and has a much smaller atomic radius than sodium and lithium. 4. Metallic Nature: Metallic nature increases down the group. The correct order should be \( Ba>K>Na \), not \( Na>K>Ba \). Thus, the incorrect arrangement is option (4) \( Na>K>Ba \).