Answer : The correct option is, (B) NaOH
Explanation :
Indicators : It is a substance that gives the visible sign by the color change of the chemical species like an acid or a base.
Universal Indicator : It changes color when mixed with an acid or base.
Universal Indicator turns red when it is added to a strong acid, it turns blue or purple when it is added to a strong base and it turns a yellowish-green when it is added to a neutral solution.
The pH range is, 1 to 14.
When the value of pH is less than 7 then the solution is acidic.
When the value of pH is more than 7 then the solution is basic.
When the value of pH is equal to 7 then the solution is neutral.
According to the pH chart, HCl is a strong acid whose pH is 1, saliva is also an acid whose pH is less than 7 that is 6.8. NaOH is a strong base whose pH is 14. The blood is slight basic in nature and the pH of blood is 7.4.
Hence, the strongest base is, (B) NaOH