: Fresh milk has a pH of 6. When milk changes into curd, the pH value will?
(A) Become 7
(B) Become less than 6
(C) Become more than 7
(D) Remain unchanged

Hint: pH is the measurement of hydrogen ion concentration in a liquid solution. This activity is directly connected to its acidic, basic and neutral characteristics.

Complete step by step answer:
> The pH is the scale used to specify how acidic or basic a water based solution is. Acidic solutions have a pH less than 7 , while basic solutions have a pH more than 7 ,at room temperature , pure water is neither acidic nor basic and has a pH of 7. pH is the measure of hydrogen ion concentration in water based solution. Very strong acids might have a negative pH, while very strong bases might have a pH greater than 14.
> pH measurements can be made using litmus paper. Most of the indicators and pH papers are useful only to tell whether a substance is acid or base. A universal indicator is a mixture of indicator solutions intended to provide a color change over a pH range of 2 to 10.
> When milk changes into curd, the pH value will change , The pH value of milk is 6 since it is acidic in nature. When the milk is converted into curd due to the action of bacteria, lactic acid is formed which is more acidic in nature. Therefore, the pH value of the milk is reduced as it turns to curd.
Therefore, option B is the answer.
Note: For many foods, the pH must be kept within a narrow range so that the food can be conserved for a longer period. For example, butter for baking bread is acidified to extend the shelf life of the bread.