Q.It is said that elemental composition of living organisms and that of inanimate objects (like earth's crust) are similar in the sense that all the major elements are present in both. Then what would be the difference between these two groups? Choose a correct answer from among the following:

• Elemental analysis of living tissue and of non-living matter such as the earth's crust turns up the same elements, so the difference cannot be about which elements are present at all.
• It shows up instead in the proportions: the earth's crust is dominated by oxygen and silicon, while living tissue is markedly richer in carbon, hydrogen and oxygen because life runs on carbon-based chemistry.
• Option (A), gold content, is not a real distinguishing feature between the two groups.
• Option (B), water content, describes a genuine difference but not the elemental-composition point the question is testing.
• Option (D), calcium content, is a minor constituent in both groups and is not the defining difference.
• Option (C) correctly names the real difference: a higher proportion of carbon, oxygen and hydrogen per unit mass in living organisms.

When the elements present in a piece of living tissue are compared with the elements present in a sample of the earth's crust, the two lists look almost identical - the same handful of elements, oxygen, silicon, carbon, hydrogen, nitrogen and so on, shows up in both. If mere presence or absence of elements were the test, living and non-living matter would appear indistinguishable.

The real difference emerges only once the elements are examined quantitatively rather than just by a checklist of what is present.

• In the earth's crust, oxygen and silicon dominate, with silicon being especially abundant in crustal rock.
• In living tissue, silicon drops to a negligible amount, while carbon, hydrogen, oxygen and nitrogen together account for the bulk of the mass.

Going through the choices: gold content (A) is not a meaningful distinguishing feature of living matter; water content (B) is a real difference but is not what "elemental composition" is asking about here; calcium content (D) is a minor constituent common to both groups, not the defining contrast. Only (C) names the true quantitative difference.

Method: Distinguish 'Which Elements' From 'How Much of Each'

This MCQ is a classic trap for students who answer too quickly, because the question itself tells you the two groups share the SAME elements — so any option implying a difference in which elements are present (or a difference unrelated to elemental composition at all) can be eliminated immediately just from re-reading the stem carefully.

Work through the options by asking, for each one, "is this actually about elemental composition, and is it actually true?" Gold content (an eliminatable option — irrelevant and not a real distinguishing feature) and calcium content (a minor constituent in both, not the defining contrast) both fail the "is this the real difference" test. Water content is a genuine difference between living and non-living matter, but it is a difference in a compound's abundance, not in the elemental composition per unit mass that the question is asking about — this is the option most likely to tempt someone who is reasoning generally about "living vs non-living" rather than reading the question's specific framing.

That leaves the option that correctly reframes the comparison as a proportional one: living organisms are not made of different elements than the earth's crust, but per unit mass they are much richer in carbon, hydrogen and oxygen — the direct consequence of life being carbon-based chemistry. When a question stem explicitly states that two things share a property (here, "all major elements present in both"), always look for the answer that engages with a DIFFERENT axis (proportion, not presence) rather than the options that contradict the stem's own premise.