Why Correct: Vitamin D deficiency causes rickets in children and osteomalacia in adults by impairing calcium absorption and bone mineralization.
Distractor Analysis: Night blindness results from Vitamin A deficiency. Scurvy is caused by Vitamin C deficiency. Hair fall can have multiple nutritional causes but is not the primary symptom of Vitamin D deficiency.
Takeaway: Vitamin A deficiency causes xerophthalmia and night blindness; Vitamin C deficiency causes scurvy; Vitamin B12 deficiency causes pernicious anemia.

Why Correct: Vitamin C is chemically ascorbic acid, a water-soluble vitamin essential for collagen synthesis, immune function, and antioxidant activity.
Distractor Analysis: Tocopherol is vitamin E, a fat-soluble antioxidant. Cyanocobalamin is vitamin B12, crucial for nerve function and red blood cell formation. Thiamine is vitamin B1, involved in carbohydrate metabolism and nerve function.
Takeaway: Vitamin C deficiency causes scurvy, characterized by bleeding gums, joint pain, and poor wound healing.

Why Correct: Vitamin K activates clotting factors II, VII, IX, and X through gamma-carboxylation, enabling calcium binding and proper blood clot formation.
Distractor Analysis: Vitamin A maintains vision and epithelial tissues. Folic acid supports DNA synthesis and red blood cell formation. Vitamin D regulates calcium and phosphate metabolism for bone health.
Takeaway: Vitamin K deficiency causes bleeding disorders like hemorrhagic disease of the newborn, treated with prophylactic vitamin K injections.

Why Correct: Nine amino acids are essential for humans: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Distractor Analysis: Six amino acids are essential for rats, not humans. Twelve represents the total number of non-essential amino acids. Fourteen would include conditionally essential amino acids like arginine and glutamine.
Takeaway: Essential amino acids cannot be synthesized by the body and must be obtained from dietary sources, while non-essential amino acids can be synthesized internally.

Why Correct: Vitamin C is scientifically named ascorbic acid, from "a-scorbic" meaning "no scurvy," as it prevents scurvy by aiding collagen synthesis.
Distractor Analysis: Acetic acid gives vinegar its sour taste and is used as a preservative. Muriatic acid is a common name for hydrochloric acid, a strong industrial acid. Lactic acid builds up in muscles during anaerobic respiration, causing fatigue.
Takeaway: Vitamin C deficiency leads to scurvy, with symptoms including bleeding gums, joint pain, anemia, and impaired wound healing due to collagen breakdown.

Why Correct: Scurvy results specifically from insufficient vitamin C, which is essential for collagen synthesis and connective tissue maintenance.
Distractor Analysis: Vitamin A deficiency causes night blindness and xerophthalmia. Vitamin B complex deficiencies cause conditions like beriberi (B1), pellagra (B3), and anemia (B12). Vitamin D deficiency causes rickets in children and osteomalacia in adults.
Takeaway: Vitamin C is also called ascorbic acid and is water-soluble; its deficiency symptoms include bleeding gums, poor wound healing, and joint pain.

Why Correct: Vitamin C (ascorbic acid) is highly sensitive to heat, oxygen, and light, making it the most labile among common vitamins.
Distractor Analysis: Vitamin A (retinol) degrades with prolonged heat but is more stable than vitamin C. Vitamin B complex includes several water-soluble vitamins (B1, B2, B3, etc.) with varying heat stability, but none are as heat-labile as vitamin C. Vitamin D (calciferol) is relatively stable to heat and oxidation.
Takeaway: Vitamin C is also destroyed by alkaline conditions and metal ions like copper and iron, which catalyze its oxidation.

Why Correct: Lysine is an essential amino acid because the human body cannot synthesize it endogenously, making dietary intake necessary.
Distractor Analysis: Rarity does not determine essentiality; some essential amino acids are common. While lysine occurs in many proteins, not all proteins contain it. All amino acids have nutritional value, but essentiality specifically refers to biosynthetic capability.
Takeaway: The nine essential amino acids for humans are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Why Correct: Pyrithiamine is a structural analog of thiamine (vitamin B1) that competitively inhibits thiamine-dependent enzymes, acting as an antivitamin.
Distractor Analysis: Beta carotene is a provitamin A precursor converted to retinol. Methylcobalamin is an active coenzyme form of vitamin B12. Folic acid is vitamin B9 itself, not an antagonist.
Takeaway: Other antivitamins include dicoumarol (vitamin K antagonist), avidin (binds biotin), and methotrexate (folic acid antagonist).

Why Correct: Pernicious anaemia results specifically from vitamin B12 deficiency due to impaired absorption, typically from autoimmune destruction of gastric parietal cells that produce intrinsic factor.
Distractor Analysis: Aplastic anaemia stems from bone marrow failure reducing production of all blood cell types. Sickle cell anaemia is a genetic hemoglobin disorder causing abnormal red blood cell shape and chronic hemolysis. Normocytic anaemia describes red blood cells of normal size but reduced number, with causes including chronic disease, blood loss, or renal failure.
Takeaway: Vitamin B12 deficiency also causes neurological symptoms like paresthesia and ataxia, while folate deficiency causes megaloblastic anaemia without neurological involvement.