Methyl Orange changes color from which to which?

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

Answer: (D)

Methyl orange is an acid–base indicator that changes color predictably with pH. In strongly acidic solutions it appears red. As the solution becomes less acidic (more basic), it shifts color through orange to yellow. This transition occurs roughly between pH 3.1 and 4.4, with the red form converting to the yellow form as pH rises. The red form is the protonated form, while the yellow form is the deprotonated form. Therefore, the color change is from red to yellow as you move from acidic to basic conditions. The option describing yellow to red would be the reverse of the usual behavior, since methyl orange does not turn blue or pink under these conditions.