What color does methyl orange indicate in an alkaline solution?

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

Answer: (A)

The test is about how pH indicators respond to acidity or basicity. Methyl orange changes color as the hydrogen ion concentration shifts: in acidic solutions it appears red, and in alkaline solutions it shifts to the yellow form. This happens because the molecule exists in a deprotonated, yellow-colored state when the solution is basic. Therefore, in an alkaline solution, methyl orange will be yellow. The other colors don’t occur for methyl orange in basic conditions, since red is seen in acidic conditions and purple or blue aren’t the typical colors produced by methyl orange.