Question

Sodium hydroxide turns blue litmus red:
(A) True
(B) False

Answer 1

Hint: To answer this question, we should know about the effect on litmus paper when we put it in acid and base. Acid and base have different effects on litmus paper.

Step by step answer:
We know that, we use litmus paper in litmus test experiments. Litmus test experiment is used to identify, whether the solution is acid or base. To perform the test we put a drop of liquid sample on a small strip of paper or dip a piece of litmus paper in a small specimen of the sample.
We will find litmus paper in either red or blue colour. We should know that, when blue litmus turns to red, it indicates that the liquid sample is acidic. Turning blue litmus red, it shows that the solution has acidity of between the pH ranges of 4.5 to 8.3. (Note that 8.3 are alkaline.) We should know that red litmus paper indicates alkalinity. By action of liquid sample on red litmus paper, if red litmus paper turns to blue it shows that liquid sample is basic. We should know that litmus paper is red below a pH of 4.5 and blue above a pH of 8.3.
There is also one more important concept that, if the paper turns purple, this indicates the pH is near neutral. Red paper that does not change colour indicates the sample is an acid. Blue paper that does not change colour indicates the sample is a base.
Now, coming back to our question we should know that sodium hydroxide is basic in nature. And from the above paragraph we can say that basic solutions turn red litmus blue. And if we use blue litmus in solution, it will remain the same. So, we can say that the above statement is false. And the correct answer is option B.

Note: We know that litmus test is quick and simple. But we should know that it is very limited. We know that it's not an accurate indicator of pH. By using litmus paper, it doesn’t give any numerical value. It only indicates that it is acid and base. One important thing that we should know that blue litmus paper turns white in chlorine gas. This colour change is due to bleaching of the dye from hypochlorite ions, not acidity/basicity