BPSC 70th CCE Prelims General Studies · Question 73 of 143

Correct — A, Tc. The symbol stands for technetium, atomic number 43, and it is the first chemical element that human beings made rather than found. Mendeleev's 1871 table had left an empty box below manganese, and he predicted the missing element under the name eka-manganese; chemists hunted for it in ores for sixty years without success, because — as is now understood — every isotope of element 43 is radioactive and none is long-lived enough to have survived in the Earth's crust from the time the planet formed. It was finally made, not found. In 1937 Carlo Perrier and Emilio Segrè, working at Palermo, examined a molybdenum foil that had been bombarded with deuterons in Ernest Lawrence's cyclotron at Berkeley and sent to Segrè on request. Molybdenum is element 42; the added proton pushed it to 43, and the two chemists separated the new activity and established that it was a new element. They named it technetium, from the Greek tekhnetos, meaning artificial — the name is itself the answer to this question. The other three symbols are ordinary naturally occurring elements dug out of minerals in the eighteenth and nineteenth centuries, and they are on the paper purely because their symbols all begin with T. Note one honest refinement: minute traces of technetium have since been detected in uranium ores, produced continuously by the spontaneous fission of uranium, so 'does not occur in nature' is better stated as 'occurs only in vanishing traces as a fission product'. That does not touch the claim being tested, which is about the first element to be prepared artificially.

• (b)Te — Tellurium, element 52 — a naturally occurring metalloid first noticed in 1782 by Franz-Joseph Müller von Reichenstein in gold ores from Transylvania and named by Martin Heinrich Klaproth from the Latin tellus, 'earth'. It is mined, not manufactured, and today comes largely as a by-product of copper refining.
• (c)Tl — Thallium, element 81 — discovered in 1861 by William Crookes, who spotted an unexpected bright green line while examining the residues of a sulphuric-acid plant with a spectroscope, and named it from the Greek thallos, a green shoot. A natural element identified by spectroscopy, and notoriously toxic.
• (d)Th — Thorium, element 90 — isolated by Jöns Jacob Berzelius in 1828 and named after the Norse god Thor. It is radioactive but entirely natural and comparatively abundant: India's monazite beach sands hold one of the world's largest reserves, which is the basis of the third stage of the Indian nuclear programme. Its radioactivity makes it the trap for anyone who equates 'radioactive' with 'man-made'.

Elements divide into those that exist on Earth because the planet formed with them and those that exist only because a laboratory made them. Everything up to uranium, element 92, occurs naturally in some quantity with two conspicuous gaps — technetium (43) and promethium (61) — whose isotopes are all radioactive with half-lives far too short to have survived the four-and-a-half billion years since the Earth's formation. Technetium was the first of the gaps to be filled artificially, in 1937, by bombarding a lighter nucleus with an accelerated particle in a cyclotron; promethium followed in 1945, identified in the fission products of a uranium reactor at Oak Ridge. Beyond uranium every element is synthetic: neptunium and plutonium in 1940, then the transuranics up to oganesson, element 118. The technique is always some form of the same thing — accelerate a projectile nucleus hard enough to fuse it with a target nucleus, then identify the tiny yield chemically or by its decay signature.

The question is a symbol test dressed as a chemistry question, and that is exactly how it should be attacked. Four symbols beginning with T: Tc, Te, Tl, Th. Translate them first — technetium, tellurium, thallium, thorium — because a candidate who cannot do that translation is choosing at random no matter how much chemistry he knows. Once translated, one name carries its own explanation: technetium is built on tekhnetos, artificial, in the same way that helium is built on helios and hydrogen on 'water-former'. Element names very often encode the discovery. The trap is thorium, and it is a good one, because thorium is radioactive and many candidates carry a loose association that radioactive implies man-made; thorium is radioactive and thoroughly natural, mined from monazite sands on the Kerala and Odisha coasts. Tellurium and thallium are pure symbol confusion — they are neither radioactive nor synthetic and are there only to punish a candidate who reads Tc as 'some T element'.

• Technetium, symbol Tc, atomic number 43, was the first artificially produced element — made in 1937 by Carlo Perrier and Emilio Segrè from a molybdenum foil bombarded with deuterons in Ernest Lawrence's Berkeley cyclotron
• Its name comes from the Greek tekhnetos, 'artificial'; Mendeleev had predicted the empty box below manganese in 1871 and called the missing element eka-manganese
• Technetium-99m is the workhorse of nuclear medicine, used in a very large share of diagnostic imaging scans because its short half-life of about six hours gives a good image with a low dose
• Promethium (61) is the other gap below uranium filled artificially, identified in 1945 in reactor fission products; every element beyond uranium (93 onwards) is synthetic
• Tellurium (1782, Müller von Reichenstein), thallium (1861, Crookes, by its green spectral line) and thorium (1828, Berzelius) are all natural elements isolated from minerals

• Reading Tc as titanium or tantalum — the symbols to keep apart are Tc technetium, Ti titanium, Ta tantalum, Te tellurium, Tl thallium, Th thorium
• Assuming a radioactive element must be artificial — thorium, uranium, radium and radon are all natural
• Saying technetium never occurs in nature at all; trace amounts arise continuously from the spontaneous fission of uranium in its ores

BPSC asks chemistry as a one-line identification and often uses the symbol rather than the name, so the item quietly tests whether you can read the periodic table's shorthand at speed. UPSC rarely asks 'which element was first', preferring applied and statement-based framings — what monazite contains, what fuels a radioisotope thermoelectric generator, why thorium is attractive as a reactor fuel — where you must judge three or four claims at once rather than recall a single name.

• practice — not a real PYQ

  The radioisotope most widely used in diagnostic nuclear-medicine imaging is

  • (a)Cobalt-60
  • (b)Technetium-99m
  • (c)Iodine-131
  • (d)Carbon-14

  Answer(b) Technetium-99m — its short half-life of about six hours and clean gamma emission make it the standard tracer for bone, cardiac and renal scans; cobalt-60 is used for radiotherapy and sterilisation, iodine-131 for thyroid disease and carbon-14 for dating.

• practice — not a real PYQ

  Which pair of elements below atomic number 92 does not occur in appreciable quantity in nature and had to be prepared artificially ?

  • (a)Technetium and promethium
  • (b)Thorium and uranium
  • (c)Radium and radon
  • (d)Polonium and francium

  Answer(a) Technetium and promethium — elements 43 and 61 are the two gaps below uranium, both filled in the laboratory; the rest listed occur naturally, several of them as members of the uranium and thorium decay series.