Given unit AT/m defines which term of magnetic circuit?

The correct answer is C, fat. A gram of fat yields about nine kilocalories, more than twice the yield of carbohydrate or protein, because its carbon chains are far less oxidised to begin with; this is also why fat is the body’s store of energy and why fatty food is called energy dense. Options A and B are wrong because carbohydrate and protein each yield about four kilocalories per gram, and protein is in any case used mainly for building and repair rather than for fuel. Option D is wrong because vitamins yield no energy at all; they are needed in milligram quantities as coenzymes and regulators, and a vitamin tablet cannot replace a meal. Water and dietary fibre likewise yield no calories, though both are necessary in the diet.

The correct answer is C, iodine. Iodine is needed to make thyroxine, the hormone of the thyroid gland; when the supply is short the gland works harder and enlarges into the swelling at the front of the neck called goitre, and in an infant the same shortage stunts growth and mental development as cretinism. This is why the law requires common salt to be iodised. Option A is wrong because an iron shortage gives anaemia. Option B is wrong because a calcium shortage weakens bone and teeth and disturbs clotting and muscle action. Option D is wrong because fluorine is the mineral whose shortage gives dental caries, while its excess in drinking water gives fluorosis, mottling teeth and deforming bone. Iodine deficiency disorders are the commonest preventable cause of mental impairment in the world.

The correct answer is B, protein. Kwashiorkor appears when a child gets enough calories but far too little protein, typically after being weaned onto a starchy gruel; the signs are swelling of the feet and face, a distended belly, thin and discoloured hair and an apathetic look, while the muscles are not severely wasted. Option A is wrong because a shortage of calories along with protein gives marasmus instead, in which the child is extremely wasted and looks old. Option C is wrong because an iron shortage gives anaemia, with pallor and tiredness. Option D is wrong because an iodine shortage gives goitre and, in a young child, cretinism. Kwashiorkor and marasmus together are called protein energy malnutrition. Pulses, milk, egg and soya are the cheap protein sources used to treat and prevent it.

The correct answer is B, A, D, E and K. These four dissolve in fat and not in water, so they travel with dietary fat, are stored in the liver and in body fat, show their deficiency only after a long shortage, and can be toxic in excess. The B complex vitamins and vitamin C are water soluble; the body cannot store them, the surplus is passed out in urine and they are easily lost in cooking water. Options A, C and D are wrong because each of them includes B or C, or both, among the fat soluble group. A simple way to remember the four is the word DAKE, or to note that they are the vitamins a person deficient in bile or fat absorption is likely to lack.

The correct answer is A, retinol. Retinol is vitamin A, and it is the raw material of rhodopsin, the pigment in the rod cells of the retina that lets us see in dim light; when it is short the eye cannot adjust to darkness, which is night blindness, and a longer shortage dries the conjunctiva as xerophthalmia and can destroy the cornea. Liver, milk and egg supply it ready made, and carrot and green leafy vegetables supply beta-carotene, which the body converts. Option B is wrong because calciferol is vitamin D, whose shortage gives rickets. Option C is wrong because tocopherol is vitamin E, an antioxidant. Option D is wrong because thiamine is vitamin B1, whose shortage gives beriberi. Night blindness is among the earliest signs of a vitamin A shortage and is reversible if treated in time.