Identify the Odd One Out among the following elements based on periodic series:
Correct Answer: Thorium (Th)
Subject: chemistry
- Cerium (Ce)
- Praseodymium (Pr)
- Gadolinium (Gd)
- Thorium (Th)
Explanation: • <b>Key Fact</b>
Thorium (Th, Z=90) belongs to the Actinide series (Period 7).
• <b>Supporting Detail</b>
Cerium (58), Praseodymium (59), and Gadolinium (64) belong to the Lanthanide series (Period 6).
• <b>Related Concept</b>
Both series belong to the f-block inner transition elements.
• <b>Why wrong options are wrong</b>
Ce, Pr, and Gd are all 4f lanthanides, while Th is a 5f actinide.
• <b>Exam Trick</b>
Lanthanides = 58 to 71; Actinides = 90 to 103.
• <b>Additional Info</b>
Thorium is named after Thor, the Norse god of thunder.