SSC
Which radioactive isotope is used to estimate the age of organic materials such as wood, paper and parchment?
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Answer: Option C — Carbon-14
Detailed Solution
Radiocarbon dating, or carbon dating, is a method of finding the age of objects that were once living, such as wood, bones, cloth, paper, parchment and charcoal. It was developed by the American chemist Willard Libby in the late 1940s, and he received the Nobel Prize in Chemistry in 1960 for it.
Carbon has three natural isotopes: carbon-12 (about 98.9%), carbon-13 (about 1.1%) and carbon-14 (a tiny trace). Carbon-12 and carbon-13 are stable, but carbon-14 is radioactive. Carbon-14 is formed continuously in the upper atmosphere when neutrons from cosmic rays strike nitrogen-14 atoms. It combines with oxygen to form carbon dioxide, which plants take in during photosynthesis. Animals take it in by eating plants. So all living things keep a nearly constant ratio of carbon-14 to carbon-12 while they are alive.
When an organism dies, it stops taking in carbon. The carbon-14 in its body then slowly decays into nitrogen-14 by beta decay, while the carbon-12 remains the same. The half-life of carbon-14 is about 5,730 years, meaning that half of it decays in that time. By measuring how much carbon-14 is left in a sample compared with a living sample, scientists can calculate how long ago the organism died. The method is useful for objects up to about 50,000 years old.
Carbon dating has been used to date the Dead Sea Scrolls, Egyptian mummies, the Shroud of Turin and material from Harappan sites.
Why not the other options?
- ✗Uranium-238 (half-life about 4.5 billion years) is used to date very old rocks and the age of the Earth.
- ✗Cobalt-60 is used in radiotherapy to treat cancer.
- ✗Iodine-131 is used to diagnose and treat thyroid disorders.
Quick tip
Remember: Carbon-14 dating = Willard Libby (Nobel 1960), half-life about 5,730 years, for once-living things. Uranium = rocks; cobalt-60 = cancer; iodine-131 = thyroid.
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Carbon & Organic Chemistry — Preparation
This question tests your understanding of Carbon & Organic Chemistry, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers carbon and its compounds: the allotropes of carbon (diamond, graphite and fullerenes), hydrocarbons, functional groups, the nomenclature of simple organic compounds, alcohols and acids, soaps and detergents, polymers and plastics. Questions commonly ask which allotrope of carbon conducts electricity (graphite), which is the hardest natural substance (diamond), what the main component of natural gas is (methane), and how soaps differ from detergents. Know the monomers of common polymers, such as ethylene for polythene, and which plastics are thermoplastics and which are thermosetting. Practise the carbon and organic chemistry questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.