Which indicator changes color from yellow to blue?

• A. Phenolphthalein
• B. Methyl Orange
• C. Bromocresol Green
• D. Phenol Red

Answer: (C)

Indicator color changes with pH; Bromocresol Green is the one that goes from yellow in acidic solutions to blue in basic solutions. As pH rises, it shifts from yellow to green and finally blue, making the yellow-to-blue transition its characteristic endpoint. Other common indicators change to different colors with pH: phenolphthalein moves from colorless to pink in basic solutions, methyl orange shifts from red in acid to yellow in base, and phenol red changes from yellow to red as pH increases. So the yellow-to-blue behavior points to Bromocresol Green.