The drops of iodine are used to detect the presence of starch in the food item. The possible reason for appearance of blue-black colour on teacher's saree is due to the presence of starch. The saree would have been starched. Paheli's socks did not have starch on it, thereby their colour did not change.

The two sources of animal fats are- Meat and cheese
(i) Meat from different animals like hens, pigs, etc.
(ii) Cheese from milk produced by cones.

Though water does not provide nutrients yet it is an important component of food because it helps
(i) to transport digested food to body cells.
(ii) to absorb nutrients from the food.
(iii) to get rid of waste products from the body.
(iv) to control and regulate the body temperature.

The major nutrients in our food are
(i) Carbohydrates       
(ii) Proteins
(iii) Fats
(iv) Vitamins
(v) Minerals
(vi) Water and roughage

Deficiency of vitamin-B₁ causes disease beri-beri.

Carbohydrate in the form of starch is tested by iodine test.

The enzymes responsible for breaking cellulose into simple forms is absent in our body.

Roughage is the fibrous matter in food which cannot be digested but is essential for body.

Vitamin-D synthesises when we are in sunlight.

No, the people of all ages and different professions require different types of nutrients according to their physical work.

No, different nutrients are available from variety of foods derived from different sources.

(i) Dal (pulses) 
(ii) Soybean

(a) The main sources of calcium minerals are milk, cheese, eggs and green vegetables. It also found in flour and bread.
It helps in formation of bone, teeth and blood clotting.
(b) Magnesium is found in cheese, green vegetable, bread and fish.
It helps in energy transfer and muscles activity. It works with calcium and vitamin-C.
(c) Potassium is found in meat, fruit, eggs, milk, etc.
The main function of potassium is balance in tissue fluid and blood. It also helps in nerve impulse conduction.
(d) Zinc is mainly found in onions, liver and green vegetables.
It works as a enzyme activator in our body.
(e) Iron is found in green vegetables, fresh fruits, etc.
Iron is needed to make haemoglobin present in red blood cells which carry oxygen from the lungs to the body parts.

(a) Boojho is suffering from night blindness.
(b) The food component which may be lacking in his diet is vitamin-A.
(c) The food items that he should include in his diet to overcome the deficiency of vitamin are carrot, papaya, milk, mango and fish oil.