A solution turns red litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
We know that, In acidic medium, red litmus doesn't change colour. In a basic medium, red litmus turns blue.In a neutral medium, red litmus doesn't change colour.Since the solution turns red litmus blue, it is basic and pH of a basic medium > 7.
Therefore, (d) is correct.