Iodine tests for:

## The reasoning The **iodine test** is a classic biochemical test that specifically detects **starch**. When you add iodine solution (usually brown) to a substance containing starch, it turns **blue-black** or dark purple. This happens because iodine molecules slip into the coiled helical structure of starch (specifically amylose), forming a complex that absorbs light differently — creating that distinctive dark color. This is the standard test in every Nigerian biology practical from JSS to SS3. If you see iodine mentioned, think starch immediately. ## Why the wrong options tempt you - **Protein** is tested using **Biuret reagent** (turns violet/purple) or **Millon's reagent** - **Sugar** (reducing sugars) uses **Benedict's solution** (turns brick-red when heated) or **Fehling's solution** - **Fat** uses the **grease spot test** (translucent spot on paper) or **Sudan III** (turns red) Students mix these up when cramming all food tests at once without linking each reagent to its specific result. ## Quick takeaway **"Iodine goes blue-black with starch — it's the only food test that produces that dark color."** Remember this visual and you'll never miss it in WAEC or JAMB practicals!