Answer: Option (b) is the correct answer.
Step-by-step explanation:
A substance that is acidic in nature will have pH less than 7 and it will turn blue litmus into red.
Whereas a substance that is basic in nature will have pH more than 7 and it will turn red litmus into blue.
And, a substance that has pH equal to 7 will be neutral in nature and it will not change the color of blue or red litmus paper.
Thus, we can conclude that when a substance is tested with litmus paper. The blue litmus paper remains blue while the red litmus paper remains red. Then it means that the substance is neutral; it is neither an acid nor a base.