Q.Which one of the following contains cobalt ?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Vitamin Classification
Water Soluble Vitamins: The First Meeting
Imagine you drop a spoonful of sugar into a glass of water. It dissolves completely, disappears into the liquid, and you can't see it anymore — but it's still there, molecule by molecule, spread evenly throughout the water. That's exactly what "water soluble" means: the substance mixes with water at the molecular level.
Now, a vitamin is a tiny organic compound your body needs in small amounts to function properly — it helps enzymes do their jobs, keeps your skin healthy, helps you see, and so on. Your body cannot make most vitamins on its own, so you must get them from food.
Put the two together: a water soluble vitamin is a vitamin that dissolves in water. This single property — solubility — determines almost everything about how these vitamins behave in your body.
The Precise Statement
Water soluble vitamins are vitamins that dissolve in water, are not stored in significant amounts in the body, and are excreted in urine when consumed in excess. They must be consumed regularly (daily or almost daily) to prevent deficiency.
The group includes the B-complex vitamins (B1, B2, B3, B5, B6, B7, B9, B12) and Vitamin C. That's 9 vitamins total.
Why Solubility Matters So Much
Think about fat. Fat and water don't mix — oil floats on top of water. Fat soluble vitamins (A, D, E, K) behave like oil: they dissolve in fat, get stored in your liver and fatty tissues, and can stay in your body for weeks or months. You don't need them every single day.
Water soluble vitamins are the opposite. Because they dissolve in water, they travel freely in your blood (which is mostly water). But your kidneys are constantly filtering your blood and removing excess water-soluble substances into urine. So if you take more Vitamin C than your body needs right now, the extra gets flushed out within hours.
This does not mean you can take unlimited amounts safely. Very high doses of some water soluble vitamins (especially B6 and niacin/B3) can cause toxicity — just not as easily as fat soluble vitamins.
The Practical Consequences
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You need them frequently — ideally every day. Missing a day won't cause immediate harm, but weeks of low intake will lead to deficiency diseases (scurvy for Vitamin C, beriberi for B1, pellagra for B3, etc.).
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Cooking destroys them — because they dissolve in water, boiling vegetables leaches vitamins into the cooking water. If you throw that water away, you lose the vitamins. Steaming or microwaving with minimal water preserves them better.
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They are fragile — heat, light, and air can break them down. That's why fresh fruits and vegetables lose vitamin content over time.
The Two Families
| Family | Members | Key Role |
|--------|---------|----------| …
Why this formula?
Vitamin Classification: Understanding the Why Behind the System
Vitamins are organic compounds that our body needs in small amounts for normal metabolism, growth, and health — but cannot synthesize in sufficient quantities. The classification system exists because it helps us understand how vitamins work and why deficiencies cause specific diseases.
Why Are Vitamins Classified This Way?
The primary classification is based on solubility — not chemical structure or function. This is because solubility determines:
- How vitamins are absorbed (with fat or water)
- How they are transported in the blood
- How they are stored in the body
- How they are excreted (risk of toxicity)
The Two Major Groups
| Group | Key Property | Why This Matters |
|---|---|---|
| Fat-soluble vitamins (A, D, E, K) | Dissolve in fats & oils | Require dietary fat for absorption; stored in liver & adipose tissue; can accumulate to toxic levels |
| Water-soluble vitamins (B-complex, C) | Dissolve in water | Absorbed directly into blood; not stored in significant amounts; excess excreted in urine (low toxicity risk) |
The Reasoning Behind Each Group
1. Fat-Soluble Vitamins (A, D, E, K)
Why they are grouped together:
- They are nonpolar molecules — they dissolve in lipids, not water.
- Absorption requires bile salts and dietary fat (emulsification).
- They travel in blood bound to carrier proteins (since blood is water-based).
- They are stored in liver and fat tissue — the body can draw on these reserves for weeks or months.
The key formula for remembering them:
All Dogs Eat Kittens
Why this matters for exams:
- Deficiency of A → night blindness (retinol needed for rhodopsin)
- Deficiency of D → rickets (calcium absorption fails)
- Deficiency of E → hemolytic anemia (antioxidant protection lost)
- Deficiency of K → bleeding (clotting factors need K)
Toxicity risk: Because they are stored, hypervitaminosis is possible (especially A and D).
2. Water-Soluble Vitamins (B-complex + C)
Why they are grouped together:
- They are polar molecules — dissolve readily in water.
- Absorption is direct into the bloodstream (no fat needed).
- They act as coenzymes — essential helpers for enzyme reactions.
- Not stored in significant amounts — excess is excreted in urine.
The key formula for remembering them:
B-complex (B₁, B₂, B₃, B₅, B₆, B₇, B₉, B₁₂) + C
Why this matters for exams:
- B₁ (thiamine) → beriberi (energy metabolism fails)
- B₃ (niacin) → pellagra (dermatitis, dementia, diarrhea)
- B₉ (folate) → neural tube defects in pregnancy
- B₁₂ (cobalamin) → pernicious anemia (needs intrinsic factor)
- C (ascorbic acid) → scurvy (collagen synthesis fails) …
Only one of these biomolecules has a metal ion built directly into its structure, and that metal is cobalt. …
Vitamin B12 (cyanocobalamin) is the cobalt-containing vitamin.
Vitamin B12 has a corrin ring with a central cobalt(III) ion coordinated to it (hence 'cobalamin'). Its deficiency causes pernicious anaemia.
…
Showing the 12 most recent of 63 on this concept.
- CBSE 2026Set 56/1/11 markMCQQ.The deficiency of which of the following vitamins causes increased fragility of red blood cells and muscular weakness : (A) Vitamin A (B) Vitamin K (C) Vitamin E (D) Vitamin D
›Reveal solutionSolution
Vitamin E acts as a membrane antioxidant protecting red blood cells from oxidative damage; its deficiency leads to hemolysis (RBC fragility) and muscular weakness. The answer is (C).
Vitamin E (tocopherol) is the body's primary lipid-soluble antioxidant, and understanding its role in cell membranes explains why its deficiency produces this specific clinical picture.
Cell membranes are rich in polyunsaturated fatty acids (PUFAs), which are highly susceptible to oxidative damage through lipid peroxidation. When free radicals attack these fatty acids, they trigger a chain reaction that destroys membrane integrity. Vitamin E sits within the lipid bilayer and interrupts this chain reaction by donating electrons to free radicals, neutralizing them before they can propagate damage.
Red blood cells are particularly vulnerable because they:
- Have high membrane surface area relative to volume
- Constantly carry oxygen, generating reactive oxygen species
- Lack a nucleus and cannot synthesize new proteins to repair damage
Skeletal muscle cells face similar oxidative stress due to their high metabolic activity and oxygen consumption.
Why each option does or doesn't fit
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Vitamin E deficiency causes the exact syndrome described. Without adequate tocopherol, RBC membranes undergo peroxidation, become fragile, and rupture easily (hemolytic anemia). Muscle cell membranes similarly deteriorate, leading to myopathy and weakness. This is seen in conditions like abetalipoproteinemia or chronic fat malabsorption.
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Vitamin A deficiency primarily affects vision (night blindness, xerophthalmia), epithelial integrity, and immune function—not RBC fragility or muscle strength directly. …
- CBSE 2026Set V11 markMCQQ.Doctor advised a 50 year old woman enough exposure to sunlight and addition of fish and egg yolk to her diet. Name the vitamin deficiency for the possible disease diagnosed by the doctor,(a) Vitamin D(b) Vitamin A(c) Vitamin C(d) Vitamin B12
›Reveal solutionSolution
The advice — sunlight plus fish and egg yolk — points to vitamin D deficiency.
Vitamin D is synthesised in the skin on exposure to sunlight (UV light) and is also obtained from dietary sources such as fish (fish-liver oils) and egg yolk. Its deficiency causes rickets in children and osteomalacia (soft, weak bones) in adults, which is a particular concern in a 50-year-old woman. …
- CBSE 2026Set DZ1 markMCQQ.Match the vitamins given in Column (I) with the diseases caused by their deficiency in Column (II): Column (I): A) Vitamin A, B) Vitamin B1, C) Vitamin C, D) Vitamin K, E) Vitamin B12. Column (II): a) Increase in clotting time of blood, b) Nightblindness, c) Beri-beri, d) Pernicious anaemia, e) Scurvy.(a) A-(d), B-(c), C-(e), D-(a), E-(b)(b) A-(b), B-(c), C-(e), D-(a), E-(d)(c) A-(a), B-(b), C-(c), D-(d), E-(e)(d) A-(b), B-(a), C-(e), D-(d), E-(c)
›Reveal solutionSolution
Matching each vitamin to its deficiency disease gives A-(b), B-(c), C-(e), D-(a), E-(d) — option (b).
Deficiency diseases of the listed vitamins:
- Vitamin A → Night blindness (also xerophthalmia) → (b)
- Vitamin B1 (thiamine) → Beri-beri → (c)
- Vitamin C (ascorbic acid) → Scurvy (bleeding gums) → (e)
- Vitamin K → poor blood clotting → increase in clotting time of blood → (a) …
- CBSE 2026Set A1 markMCQQ.Vitamin B12 contains(a) Cobalt(b) Magnesium(c) Iron(d) Nickel
›Reveal solutionSolution
Vitamin B12 (cyanocobalamin) is a cobalt-containing vitamin.
Vitamin B12, cyanocobalamin, is the only vitamin that contains a metal ion. Its structure has a corrin ring (similar to a porphyrin) with a central cobalt atom. A deficiency causes pernicious anaemia. (By comparison, chlorophyll contains magnesium …
- CBSE 2026Set A1 markMCQQ.Riboflavin is the chemical name of which of the following ?(a) Vitamin B1(b) Vitamin B2(c) Vitamin B6(d) Vitamin B complex
›Reveal solutionSolution
Riboflavin = vitamin B2.
Riboflavin is the chemical (systematic) name for vitamin B2, a water-soluble vitamin important in energy metabolism; its deficiency causes cheilosis and cracking/sores at the corners of the mou …
- CBSE 2026Set ANNUAL1 markQ.Scurvy disease is caused by the deficiency of Vitamin ______ (fill in the blank).
›Reveal solutionSolution
Scurvy, characterised by bleeding gums and poor wound healing, results from a deficiency of vitamin C (ascorbic acid), which is …
- CBSE 2026Set ANNUAL1 markQ.Write the name of any one source of vitamin A.
›Reveal solutionSolution
Vitamin A (retinol) is a fat-soluble vitamin obtained from animal sources directly, or from plant sources as its precursor, beta-carotene.
Vitamin A can be obtained from foods in two forms:
- Preformed Vitamin A (retinol), found in animal sources such as fish liver oil, egg yolk, butter, and milk.
- Provitamin A (beta-carotene), found in plant sources such as carrots, which the body converts into active Vitamin A. …
- CBSE 2026Set ANNUAL1 markMCQQ.Riboflavin is the chemical name of:(a) Vitamin B1(b) Vitamin B2(c) Vitamin B6(d) Vitamin B12
›Reveal solutionSolution
Riboflavin is the chemical/common name for Vitamin B2, a water-soluble B-complex vitamin.
Vitamins are classified by solubility into fat-soluble (A, D, E, K) and water-soluble (B-complex, C). Among the B-complex vitamins, each has both a chemical name and a number:
- Vitamin B1 = Thiamine
- Vitamin B2 = Riboflavin
- Vitamin B6 = Pyridoxine
- Vitamin B12 = Cyanocobalamin …
- CBSE 2026Set ANNUAL1 markMCQQ.Mohan cannot visualise properly in night. This disease is due to the lack of which vitamin?(a) Vitamin A(b) Vitamin C(c) Vitamin B(d) Vitamin D
›Reveal solutionSolution
Deficiency of Vitamin A causes night blindness (nyctalopia).
Vitamin A (retinol) is essential for synthesising the visual pigment rhodopsin in the retina's rod cells, needed for vision in dim light. A deficiency of vitamin A impairs rhodopsin regeneration, leading to difficulty seeing in low light/at night — a condition called …
- CBSE 2026Set ANNUAL1 markQ.Write answer in one word/sentence: Write the chemical name of Vitamin B2.
›Reveal solutionSolution
Vitamin B2 is chemically named riboflavin.
Vitamin B2 is a water-soluble vitamin of the B-complex group; its chemical name is riboflavin. Its deficiency causes chei …
- CBSE 2026Set ANNUAL1 markQ.Name the vitamin whose deficiency causes poor coagulation of blood.
›Reveal solutionSolution
Vitamin K is the fat-soluble vitamin required for normal blood coagulation, so its deficiency causes poor clotting.
Vitamins are grouped as fat-soluble (A,D,E,K) and water-soluble (B-complex and C). Vitamin K plays a key role in the biosynthesis of the clotting factor prothrombin in the liver. Without adequate vitami …
- CBSE 2025Set X11 markMCQQ.Incorrect statement regarding vitamins,(a) Excess vitamin intake is harmful(b) Most of the vitamins contain amino groups(c) Vitamins can be produced by plants(d) Vitamin deficiency causes diseases
›Reveal solutionSolution
The false statement is (b) — most vitamins are NOT amines; they are a chemically diverse class and only a handful contain amino groups.
Evaluating each statement:
- (a) Excess vitamin intake is harmful — TRUE. Fat-soluble vitamins (A, D, E, K) are stored in the body and excess intake causes hypervitaminosis (toxicity).
- (b) Most of the vitamins contain amino groups — FALSE. Vitamins are chemically very varied (e.g. vitamin C is an acid/lactone, vitamin A is an alcohol, vitamin D is a steroid derivative). Only a few (e.g. some B-group vitamins like B1, B6, B12) contain nitrogen/amino groups — they are the exception, not the majority. The word "vitamine" was coined historically because the first one studied contained an amine, but this does not hold for most vitamin …
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