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Protium, deuterium and tritium are:
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Answer: Option C — Isotopes of hydrogen
Detailed Solution
Isotopes are atoms of the same element that have the same atomic number (the same number of protons) but different mass numbers, because they have different numbers of neutrons. Since the number of protons and electrons is the same, isotopes of an element show almost the same chemical properties, but their physical properties, such as mass and density, differ.
Hydrogen has three natural isotopes. Each has one proton and one electron:
Protium (hydrogen-1) has no neutron. It makes up about 99.98% of natural hydrogen and is the only common atom with no neutron at all.
Deuterium (hydrogen-2, symbol D) has one neutron. It is also called heavy hydrogen. Water made with deuterium, D2O, is called heavy water. Heavy water is used as a moderator in many nuclear reactors, including India's pressurised heavy water reactors, to slow down neutrons.
Tritium (hydrogen-3, symbol T) has two neutrons. It is radioactive, with a half-life of about 12.3 years, and emits beta particles. It is used in self-luminous signs and watch dials and is an important fuel in nuclear fusion research.
Deuterium and tritium together are the fuel for fusion reactions planned in projects such as ITER, in which India is a partner.
Why not the other options?
- ✗Isobars are atoms of different elements with the same mass number, such as argon-40 and calcium-40.
Allotropes are different physical forms of the same element in the same state, such as diamond and graphite (carbon). Hydrogen's forms protium, deuterium and tritium are not allotropes.
Isotones are atoms with the same number of neutrons but different numbers of protons; the three forms of hydrogen have different neutron numbers.
Quick tip
Remember: Hydrogen isotopes = protium (0 neutrons), deuterium (1 neutron, heavy water D2O) and tritium (2 neutrons, radioactive). Isotopes = same atomic number; isobars = same mass number.
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Atomic Structure — Preparation
This question tests your understanding of Atomic Structure, 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 the structure of the atom: the discovery of subatomic particles, the atomic models of Dalton, Thomson, Rutherford and Bohr, atomic number and mass number, isotopes, isobars and isotones, electronic configuration and valency. Questions commonly ask which scientist proposed which model, what Rutherford's gold foil experiment showed (a small, dense, positively charged nucleus), and how isotopes differ from isobars. For example, isotopes have the same atomic number but different mass numbers. Practise working out the number of protons, neutrons and electrons from given numbers. Practise the atomic structure 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.