Phenol Red changes color from yellow to which color?

• A. Red
• B. Blue
• C. Yellow
• D. Pink

Answer: (A)

Phenol red is an acid–base indicator. Its color depends on the protonation state: in acidic solutions it looks yellow, and as the solution becomes basic it shifts toward red within its visible transition range (roughly pH 6.8 to 8.4). So when it changes from yellow, the next color you’d see is red. (Blue isn’t part of its typical transition, and pink would appear only at very high basicity beyond the main range.)