Which of the following vitamins are water soluble ?

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Correct — D, None of these. Vitamins are sorted into exactly two groups by the solvent in which they dissolve, and the division is absolute: the FAT-soluble vitamins are A, D, E and K, and the WATER-soluble vitamins are the eight B-complex vitamins together with vitamin C. All three substantive options on this page — Vitamin K, Vitamin A and Vitamin D — belong to the fat-soluble group, so not one of them answers the question and the escape option is the only response left. That is the whole logic of the item, and it is worth seeing why the three were chosen: they are A, D and K, which is three-quarters of the fat-soluble set, with only vitamin E left out. The distinction is not a filing convenience. Fat-soluble vitamins are absorbed with dietary fat, travel in chylomicrons through the lymphatic system, and are stored in the liver and in adipose tissue, so they need not be eaten daily and, taken in excess, they accumulate — hypervitaminosis A and hypervitaminosis D are real toxic states. Water-soluble vitamins are absorbed directly into the portal blood, are held in the body only in small amounts, and any surplus is filtered out by the kidneys and lost in urine, so they must be supplied regularly and are very hard to overdose on. Vitamin B12 is the one partial exception: it is water-soluble but the liver stores enough of it to last several years. Two of the three named options have their own giveaway properties: vitamin D is the vitamin the skin manufactures itself from a cholesterol precursor on exposure to ultraviolet B, and vitamin K is largely supplied by bacteria in the large intestine and is required for the liver to make prothrombin and the other clotting factors — neither behaviour is possible for a vitamin that is simply washed out in urine.

Why the other options are wrong — (a) Fat-soluble. Vitamin K — phylloquinone from green leafy vegetables and menaquinone from gut bacteria — is the coagulation vitamin, needed for the liver to synthesise prothrombin and the other vitamin-K-dependent clotting factors. Its deficiency shows as delayed clotting and bleeding, which is why newborns are routinely given a vitamin K injection.  (b) Fat-soluble, and the classic example of a stored vitamin — the liver holds enough to last months, which is why a single high-dose supplement can protect a child for six months. Deficiency causes night blindness and, in its severe form, xerophthalmia; excess causes hypervitaminosis A, a genuine toxicity that would be impossible if the vitamin were flushed out in urine.  (c) Fat-soluble, and strictly a prohormone rather than a dietary essential in the ordinary sense — the skin makes cholecalciferol from 7-dehydrocholesterol under ultraviolet B light. Its deficiency causes rickets in children and osteomalacia in adults; because it is stored rather than excreted, excess intake causes hypercalcaemia.

Concept: A vitamin is an organic compound the body needs in small quantity but cannot synthesise in adequate amount, so it must come from the diet. Thirteen are recognised for humans, and the standard classification splits them by solubility because solubility governs everything else about how the body handles them — absorption, transport, storage, excretion and the shape of both deficiency and toxicity. The four fat-soluble vitamins, A, D, E and K, ride with dietary lipids, are stored, and can therefore be both hoarded and overdosed. The nine water-soluble vitamins — B1 thiamine, B2 riboflavin, B3 niacin, B5 pantothenic acid, B6 pyridoxine, B7 biotin, B9 folate, B12 cobalamin and C ascorbic acid — dissolve in plasma, are turned over quickly and are lost in urine, which is why their deficiency diseases appear comparatively fast on a poor diet and why cooking water can strip them out of food.

State PCS 2025 Q40 — Science & Technology PYQ with Answer

State PCS 2025 Q40 — Science & Technology PYQ with Answer