A student tests an unknown solution using universal indicator and litmus paper. The universal indicator turns orange and the litmus paper turns red. Describe what these results tell the student about the unknown solution, and explain why scientists prefer to use universal indicator rather than litmus paper when testing solutions.

The universal indicator turns orange, which lies between yellow and red on the colour chart, indicating a pH of about 4–5 – a weakly acidic solution. The litmus paper turns red, confirming that the solution is acidic but giving no further detail. Scientists prefer universal indicator because it is a mixture of dyes that changes through a continuous range of colours, allowing the pH value or the relative strength of the acid to be estimated. Litmus paper only shows a binary acidic/alkaline result and cannot provide a pH value.