Final answer:
In an acidic solution, blue litmus paper will turn red, indicating the presence of an acid. The correct answer to the student's question is (b) The paper will turn red. Red litmus paper remains unaffected in acidic solutions.
Step-by-step explanation:
When litmus paper is dipped in an acidic solution, the color change you observe is dependent on the initial color of the litmus paper. In case you start with blue litmus paper, the acidic environment will cause the paper to turn red (b) The paper will turn red). This happens because acids characteristically turn blue litmus paper red. However, if you start with red litmus paper, there will be no color change since red litmus paper remains red in acidic conditions.
It's also interesting to note that while acids result in this color change for litmus paper, basic or alkaline substances have the opposite effect. They turn red litmus paper to blue. The litmus paper does not change the color of the solution; instead, its own color changes in response to the solution's pH level. This makes litmus paper a useful indicator for distinguishing between acidic and basic solutions.