Question

Which isotope of hydrogen is/are radioactive in nature?
(A) Protium and deuterium
(B) Tritium only
(C) Tritium and deuterium
(D) Only deuterium

Answer 1

Hint: Two or more atoms have the same atomic number and different mass numbers then they are called isotopes. Hydrogen has three isotopes, hydrogen, deuterium and tritium. They can be represented as follows. Hydrogen - ${}_1^{1}H$ , Deuterium- ${}_1^{2}H$ and Tritium- ${}_1^{3}H$ . They have the same atomic number but different mass numbers.

Complete step by step solution:
-The substances which have unstable nuclei undergo decay and form stable nuclei.
-This type of substance is called radioactive substances. In the decay process, radioactive elements emit radiation in the form of alpha, beta and gamma rays.
-Hydrogen ( ${}_1^{1}H$ ) is also called protium.
-Protium contains one proton and one neutron in its nucleus.
-Tritium ( ${}_1^{3}H$ ) contains one proton and two neutrons in its nucleus and it is unstable in nature.
-Because the less stable tritium undergoes radioactive decay and converts into helium by emitting a beta particle.
-We can represent the decay of tritium as follows.
$${}_1^{3}H\stackrel{-\beta }{\to }{}_2^{3}He+{}_{-1}\beta$$
-Therefore tritium is the radioactive element among the isotopes of the hydrogen.

So, the correct option is B.

Note: If any element has an excess number of neutrons in their nuclei then they undergo radioactive decay to get the stability. In the process of radioactive decay, the radioactive element may undergo a decay process once or twice depending upon the number of protons and neutrons present in the nucleus.