Consider the following elements found in a typical 70 kg man and arrange them in correct increasing order. 1. Sodium 2. Potassium 3. Copper 4. Iron Select the correct answer from the code given below : Code :
- (a)4, 3, 1, 2
- (b)3, 4, 1, 2
- (c)3, 4, 2, 1
- (d)4, 3, 2, 1
Correct — B, 3, 4, 1, 2 (Copper < Iron < Sodium < Potassium). On the standard reference figures for a 70 kg human body, copper is about 72 milligrams, iron about 4.2 grams, sodium about 100 grams and potassium about 140 grams. So the order from smallest to largest mass is copper, then iron, then sodium, then potassium — that is, statements 3, 4, 1, 2. The two decisive facts are that iron outweighs copper by roughly sixty times (both are trace elements, but not equally trace), and that potassium outweighs sodium in the body as a whole.
- (a)4, 3, 1, 2 — It gets the top of the order right (sodium then potassium) but puts iron below copper. The body carries about 4.2 g of iron against about 72 mg of copper — a roughly sixty-fold gap — so iron can never be the smallest of the four. Candidates fall into this by treating 'trace element' as a single tier.
- (c)3, 4, 2, 1 — It gets the bottom right (copper then iron) but reverses the top, placing potassium below sodium. In blood plasma sodium is indeed the dominant ion, but the question is about the WHOLE body: potassium (about 140 g) sits mainly inside cells, and intracellular volume far exceeds extracellular fluid, so total-body potassium exceeds total-body sodium (about 100 g).
- (d)4, 3, 2, 1 — This is the completely inverted order — it reverses both pairs at once, putting iron below copper and potassium below sodium. It is what a candidate marks when they read the codes as decreasing order rather than increasing.
About 96% of body mass is just four elements — oxygen, carbon, hydrogen and nitrogen. The rest is minerals, graded by quantity: macro-minerals present in tens or hundreds of grams (calcium about 1 kg, potassium about 140 g, sodium about 100 g, magnesium about 19 g) and trace elements present in grams or milligrams (iron about 4.2 g, zinc about 2.3 g, copper about 72 mg). Calcium is the most abundant mineral in the body, locked up mainly in bone. These reference values are the widely used figures for a 70 kg adult male.
The trap in this question is the sodium-potassium pair, and it is a good trap because it punishes half-knowledge. Every student learns that sodium is the chief EXTRACELLULAR cation and potassium the chief INTRACELLULAR cation, and that plasma sodium (about 140 mmol/L) far exceeds plasma potassium (about 4 mmol/L). But the intracellular compartment is roughly twice the volume of the extracellular one, so once you count the whole body, potassium wins. Reasoning route: fix copper as the smallest (milligrams, an enzyme cofactor), iron next (grams, mostly in haemoglobin and myoglobin), and then decide the sodium-potassium pair by remembering it is a total-body count, not a blood test.
- Reference figures for a 70 kg body: copper about 72 mg, iron about 4.2 g, sodium about 100 g, potassium about 140 g
- Calcium is the most abundant mineral in the body at about 1 kg, mostly as hydroxyapatite in bone and teeth
- Iron is largely bound in haemoglobin and myoglobin; copper works as a cofactor in enzymes such as cytochrome c oxidase and superoxide dismutase
- Sodium is the principal extracellular cation and potassium the principal intracellular cation — but total-body potassium still exceeds total-body sodium
- Oxygen, carbon, hydrogen and nitrogen together make up about 96% of body mass
Increasing order = copper, iron, sodium, potassium = 3, 4, 1, 2. The highlighted row is where the question is won: potassium beats sodium over the whole body even though sodium dominates the blood.
- Carrying plasma concentrations into a total-body question and concluding sodium exceeds potassium
- Treating all trace elements as equal — iron is present in grams, copper only in milligrams
- Misreading 'increasing' as 'decreasing' and marking the exactly reversed code
UPPSC asks for the ordering or the ranking of body elements; UPSC prefers the functional angle — which mineral is needed for muscle contraction, which protein carries iron, what a given deficiency causes.
Consider the following minerals: 1. Calcium 2. Iron 3. Sodium Which of the minerals given above is/are required by human body for the contraction of muscles?
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer(d) 1, 2 and 3
The same set of body minerals approached from the other side. UPPSC asks how MUCH of each element the body holds; UPSC asks what calcium, iron and sodium are FOR — calcium triggering the contraction, sodium carrying the action potential, iron supplying the oxygen-linked energy. Quantity plus function is the full picture for this topic.
Which of the following natural substances contains iron (Fe) ?
- (a) Chlorophyll
- (b) Collagen
- (c) Keratin
- (d) Myoglobin
Answer(d) Myoglobin
Directly on the iron half of this ordering: myoglobin is one of the two iron proteins (with haemoglobin) that account for most of the roughly 4.2 g of iron in the body — which is exactly why iron outranks copper here.
- practice — not a real PYQ
Which of the following is the most abundant mineral element in the human body by mass?
- (a)Iron
- (b)Sodium
- (c)Calcium
- (d)Potassium
Answer(c) Calcium — about 1 kg in a 70 kg adult, mostly as hydroxyapatite in bone and teeth; potassium (about 140 g) and sodium (about 100 g) are far behind.
- practice — not a real PYQ
Consider the following statements: 1. Potassium is the principal cation of the intracellular fluid. 2. Sodium is the principal cation of the extracellular fluid. Which of the statements given above is/are correct?
- (a)Only 1
- (b)Only 2
- (c)Both 1 and 2
- (d)Neither 1 nor 2
Answer(c) Both 1 and 2 — the gradient is maintained by the sodium-potassium pump and underlies the resting membrane potential.