From the following which isotope is called as heavy hydrogen ?
(a) Protium
(b) Deuterium
(c) Tritium
(d) None of the above
Answer options :

Question

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Correct — option (2), 'Only (b)', deuterium. Hydrogen has three isotopes, all with a single proton and therefore all chemically hydrogen, differing only in the number of neutrons in the nucleus. Protium, written as hydrogen-1, has no neutron at all and is by far the most abundant form. Deuterium, hydrogen-2, written D, has one neutron, so its atom is about twice as massive as an ordinary hydrogen atom, and that doubling of mass is what earned it the name heavy hydrogen. Tritium, hydrogen-3, has two neutrons and is radioactive, decaying with a half-life of about twelve years, and it occurs only in traces. The name matters in practice because of the compound it forms: water made with deuterium in place of ordinary hydrogen is heavy water, whose formula is written D2O, and heavy water is the moderator and coolant of the pressurised heavy water reactors that form the first stage of India's nuclear power programme. A moderator slows fast neutrons so that they can sustain fission in natural uranium, and heavy water performs that task while absorbing very few neutrons, which is why a reactor using it can run on unenriched uranium. Deuterium was identified by Harold Urey in the early 1930s, work for which he received the Nobel Prize in Chemistry, and it makes up only a very small fraction of natural hydrogen, of the order of a hundredth of one per cent, so heavy water has to be concentrated from ordinary water by industrial plants rather than mined.

Why the other options are wrong — (a) Tritium is the heaviest of the three isotopes, with two neutrons, but it is not the one called heavy hydrogen. It is distinguished instead by being radioactive — the only unstable isotope of hydrogen — with a half-life of about twelve years, and it occurs in nature only in traces produced by cosmic rays in the upper atmosphere. A candidate reasoning that the heaviest isotope must be the one named heavy hydrogen will pick this option; the name, however, belongs by long-established usage to deuterium, the isotope whose compound heavy water is a staple of nuclear technology.  (c) Choosing 'none of the above' asserts that no printed isotope answers the question, which cannot stand once deuterium has been recognised. An escape option is only worth taking when each substantive choice has been positively ruled out, and here the second of the three is not merely defensible but is the standard name in chemistry and in the nuclear industry alike. This option catches the candidate who cannot recall which isotope carries the name and prefers to avoid the choice rather than reason from the mass numbers, which settle it directly.  (d) This option names protium and tritium and misses deuterium entirely, so it is wrong at both ends. Protium is the ordinary, lightest isotope with no neutron and could not be called heavy anything, while tritium is the radioactive isotope, notable for its instability rather than for a special name. The option also asks for two isotopes when the question, by its phrasing, expects a single one — a question that asks which isotope is called heavy hydrogen is not looking for a pair.

Concept: Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, so they occupy the same place in the periodic table and behave nearly identically in chemistry while differing in mass and in nuclear stability. Hydrogen is the textbook case because its three isotopes differ so much in relative mass — one, two and three units — that they are given individual names, which happens with no other element. Protium, with a lone proton, accounts for almost all natural hydrogen. Deuterium adds a neutron and is stable; its oxide, heavy water, is denser than ordinary water, freezes and boils at slightly higher temperatures, and is separated industrially from ordinary water. Tritium adds a second neutron, is radioactive with a half-life of about twelve years, and is produced both naturally by cosmic radiation and artificially in reactors. The nuclear significance of the isotopes runs in two directions. In fission reactors, heavy water serves as a moderator that slows neutrons without absorbing many of them, which allows natural uranium to be used as fuel — the basis of the Indian pressurised heavy water reactor fleet. In fusion, the reaction most studied for future power generation is that between deuterium and tritium, which is why both isotopes appear in discussions of thermonuclear energy.

State PCS 2024 Q69 — Science & Technology PYQ with Answer

State PCS 2024 Q69 — Science & Technology PYQ with Answer