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

Question

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 :

UnlockIAS · Accepted Answer

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.

Why the other options are wrong — (a) 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) 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) 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.

Concept: 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.

State PCS 2025 Q84 — Science & Technology PYQ with Answer

State PCS 2025 Q84 — Science & Technology PYQ with Answer