Choose the odd term: Thyroxine, Adrenaline, and Insulin are hormones; Iodine is a chemical element (nutrient), not a hormone. Identify the outlier.

Introduction / Context:
Biology/chemistry classification contrasts biochemical messengers with a chemical element.

Given Data / Assumptions:

• Thyroxine, Adrenaline, Insulin → hormones secreted by endocrine glands.
• Iodine → trace element required for thyroid hormone synthesis, not itself a hormone.

Concept / Approach:
Group by functional role in physiology: messenger hormone vs essential nutrient element.

Step-by-Step Solution:

Verification / Alternative check:
Thyroxine contains iodine atoms, yet iodine is the raw element, not a secreted messenger.

Why Other Options Are Wrong:
They are authentic hormones.

Common Pitfalls:
Confusing “component of a hormone” (iodine in thyroxine) with “is a hormone.”

Final Answer:
Iodine is the odd term.