Question

The isotopes of hydrogen are:
(A) Tritium and Protium only
(B) Deuterium and tritium only
(C) Protium and deuterium only
(D) Protium, deuterium and tritium

Answer 1

Hint: It is a factual type question, where we have to name the isotopes of hydrogen atoms.
- Hydrogen atoms have atomic number one and mass number one.
- The isotopes are those atomic species which possess the same atomic number, but have different atomic mass i.e. they have the same number of electrons and protons, but differ in number of neutrons.

Complete Solution :
So in the question we are asked to name the isotopes of hydrogen atoms.
- Before directly going into the solution for the question, let’s brush up our memory about Hydrogen.
- Hydrogen possesses the atomic number 1 and it is represented as H. It is the first element of the periodic table and kept along with the s –block elements. H has an atomic weight of 1.008 and which is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the universe, which constitutes roughly 75 % of all the baryonic mass.
- At normal temperature and pressure, hydrogen exists as a non-toxic, colourless, odourless, tasteless, non-metallic, highly combustible diatomic gas. Its molecular formula is ${{H}_{2}}$.Hydrogen easily forms covalent compounds with most of the non-metallic elements. Hence, most of the hydrogen on Earth will be present in their molecular forms like water, organic compounds etc.
- Hydrogen also plays a vital role in acid–base reactions, since most of the acid-base reactions involve the exchange of protons between soluble molecules.
- Now let’s take a look at the naturally occurring isotopes of H atoms, as we know that the isotopes of those species only differ by the mass number or say in the number of neutrons present in them.
- The naturally occurring isotopes of hydrogen are protium, deuterium and tritium. These three are the most common isotopes since they have a name.
- Protium and deuterium isotopes are more stable than the third isotope, tritium. Tritium has a half-life of about 12.32 years.
- Among the three isotopes, protium is the most common one and it is represented as$^{1}H$, it is called so since it has only one proton in them. In protium there is one electron, one proton and no neutron.
- Deuterium is represented by D or$^{2}H$, it has one proton, one electron and one neutron. Hence it will have a mass approximately equal to 2.
- Tritium is represented as $^{3}H$ or T. It is one of the stable radioactive isotopes among the other radioisotopes of hydrogen atoms. In tritium there is one electron, one proton and two neutrons and hence has an atomic mass equals to three.
So, the correct answer is “Option D”.

Note: There is also many other isotopes for hydrogen which is artificially synthesized like $^{4}H{{,}^{5}}H{{,}^{6}}H$ and $^{7}H$. Majority of the artificially synthesized isotopes are radioactive in nature and are unstable and do not exist naturally in nature. Tritium is the most stable radioactive isotope which occurs naturally and is stable.