Methyl orange is red in a solution, but it becomes yellow when base is added slowly. What does this show?

Correct answer: Acidity decreased and the solution became basic or nearly neutral

Methyl orange is an acid-base indicator: it appears red in a sufficiently acidic medium and yellow in a neutral or alkaline medium. Adding a base consumes some of the acid, so the hydrogen-ion concentration decreases and the pH rises. The colour change therefore shows movement from acidic conditions toward neutral or basic conditions. It does not indicate metal formation, carbon dioxide formation, or increasing acidity. Hence option A is correct.