The translucency spot in food test shows the presence of

Analyze the question: The "translucency test" (also called the grease spot test) is a food test. We need to identify which food class it detects.

Explain the concept: Fats and oils are lipids. They are not absorbed by paper the way water is, and they leave a stain that lets light pass through.

The test:

1. Rub a small amount of the food sample (or a few drops of oil) on a piece of unglazed or brown paper.
2. Allow it to dry. Water-based substances evaporate and leave no mark.
3. Hold the paper up to the light.

Observation: A translucent (semi-transparent) greasy spot that does not disappear on drying shows that fat or oil is present.

Checking the other options:

• Starch: tested with iodine solution, which turns blue-black.
• Water: tested with anhydrous copper(II) sulphate (white to blue) or cobalt chloride paper (blue to pink).
• Protein: tested with Biuret reagent (purple/violet) or Millon's test (red/pink).

Answer: The translucent spot test shows the presence of fats, which is option A.

Tip: Think "translucent = lipid", since the grease makes the paper see-through. Also remember the other tests as a set: iodine for starch, Benedict's for reducing sugar, Biuret for protein, and the ethanol emulsion test for fats (a milky white emulsion). A common exam trap is mixing up the ethanol emulsion test and the translucent spot test, but both detect fats and oils.