Question

A solution turns red litmus blue; its pH is likely to be:
A.1
B.4
C.5
D.10

Answer 1

Hint: pH is the measure of how much a substance is acidic or basic. It is used to identify the degree of acidity or basicity by the change of colours.

Complete step by step answer:
-pH is a measure which shows how acidic/basic any substance is. Its range goes from 0 to 14 with 7 being the neutral point.
-If the pH value of any substance is greater than or equal to 0 and less than 7, then the substance is said to be acidic.
-If the pH value of any substance is greater than 7 and less than or equal to 14, then the substance is said to be basic.
-If the pH value of any substance is equal to 7, then the substance is said to be neutral.
-The lower the pH value, the stronger will be the acid and the higher the pH value the stronger the base will be.
-Whether a substance is acidic or basic, can also be found out with the help of a litmus paper. There are two types of litmus paper: blue litmus paper and red litmus paper.
-A blue litmus paper turns red in acidic conditions but has no effect in basic condition and this shows that the pH will be less than 7.
-A red litmus paper turns blue under basic conditions and has no effect under acidic conditions and this shows that the pH is greater than 7.
-Both the litmus papers turn purple when the substance is neutral.

Now, it is given in the question that red litmus paper turns blue. This means that the conditions should be basic for this to happen. Thus, the pH should be greater than 7.

Hence, the correct answer is option (D) 10.

Note: The pH is also used to measure the concentration of free ${H}^{+}$ ions in the solution. The lower the pH, the higher will be the concentration of the ${H}^{+}$ ions and vice-versa.