Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? 

The pH is a scale that defines whether the substance is acidic or basic in nature. For acidic substances, pH <7, for basic substances pH>7, for neutral substances, pH = 7.

Fresh milk has lactic acid, due to which it is slightly acidic with pH 6.

Now, the milk changes into curd due to the action of lactobacillus bacteria on the milk protein casein. During this process, more lactic acid is produced, and thus milk changes into curd by fermentation.

As more acid is produced, thus, the pH of the milk will decrease after changing into the curd.

Hence, the correct option is (B).