a) Fresh milk contain harmful microbes so they should be boiled before consumption but processed milk stored in packets are pasteurized where microbes are killed hence they can be consumed before boiling.

Pasteurization is the process of heating a foodstuff like milk at a very high temperature and then cooling it rapidly. This process kills most of the microbes present in food stuff.

b) Raw fruits and vegetables get easily contaminated by microbes which spoil them. So freezing them in the refrigerator we can prevent their spoilage as low temperature inhibits the growth of microbes.

But jam and pickles are added with preservatives that prevent the growth of microbes even without refrigeration.

c) Farmers prefer to grow beans and peas in nitrogen deficient soils as they are leguminous plants and their root nodules contain nitrogen-fixing bacteria rhizobium which fixes atmospheric nitrogen into nitrites and nitrates and enriches the soil with nitrogen and increases its fertility.

d) Though mosquitoes do not live in water their larvae grow in water. So stagnant water serve as a good breeding place for mosquitoes. So if water is not allowed to stagnant mosquitoes cannot lay eggs and their larvae cannot survive.