If a solution turns blue litmus red, its pH is likely to be:

Since blue litmus paper turns red in an acidic solution, the solution that turns blue litmus paper red is likely to be acidic. Therefore, the pH of the solution would be less than 7. Among the given options, 6 is the closest value below 7, making it the most likely answer. While the exact pH might not be precisely 6, it falls within the acidic range (less than 7) based on the litmus paper test.