$A$ milkman adds a very small amount of baking soda to fresh milk.
$(a)$ Why does he shift the $pH$ of the fresh milk from $6$ to slightly alkaline?
$(b)$ Why does this milk take a long time to set as curd?

(N/A) The milkman shifts the $pH$ of the fresh milk from $6$ to slightly alkaline to prevent the milk from turning sour quickly. In an alkaline condition,the growth of lactic acid-producing bacteria is inhibited,which prevents the milk from spoiling.
$(b)$ Since this milk is slightly basic,the lactic acid produced by bacteria during the fermentation process is neutralized by the added baking soda. Therefore,it takes a longer time for the milk to reach the required acidity level to set as curd.