Diffusion visualization using pH indicator

Steps:

• Prepare acidic agar with colorless indicator; remove central 1 cm disc to form well.
• Place petri dish over card with 1 cm concentric circles for measurement.
• Add alkali to well; it diffuses outward, turning agar pink where pH rises.
• Measure pink ring radius over time against card lines to track diffusion rate.

Why C is correct:

• C describes pink color spreading in concentric rings matching card lines, aligning with Fick's law of diffusion where concentration gradient drives radial spread.

Why the others are wrong:

• A: No color change expected without alkali addition.
• B: Color remains colorless as acid dominates initially.
• D: Lines measure diffusion, not just well size.

Not enough information on exact choices, but C fits standard observation.

Final answer: C