Answer:
An acid solution.
Explanation:
The litmus paper is an acid-base indicator, its colors change depending on the pH of the solution. If the pH < 4.5, the litmus paper turns red, if the pH> 8.3 the litmus paper turns blue.
If the pH > 7, there is a base solution, if the pH< 7 there is an acid solution, and if the pH = 7 its a neutral solution.
So, if the litmus paper turned red, the solution has pH<4.5, and it's an acid solution.