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What color change does an acid produce on blue litmus paper?

  1. Green

  2. Yellow

  3. Red

  4. No change

The correct answer is: Red

When an acid is introduced to blue litmus paper, it causes a color change that results in the paper turning red. This reaction occurs because litmus paper is a pH indicator, and acids, which are substances with a pH less than 7, specifically react with the dye used in the litmus paper. The blue dye changes to red in the presence of acidic conditions, effectively signaling the acidity of the solution. This property of litmus paper is widely utilized in various chemical applications to quickly assess the pH of a solution without the need for complex equipment. Therefore, when dealing with an acidic substance, the expected and observed change on blue litmus paper is a shift to red, confirming the presence of an acid.