Question

The isotope of hydrogen which is radioactive is …………………..
$
  (a){\text{ Trithium}} \\
  (b){\text{ Deuterium}} \\
  (c){\text{ Nacent hydrogen }} \\
  (d){\text{ Parahydrogen}} \\
$

Answer 1

Hint – In this question use the concept that hydrogen has three isotopes : Protium, deuterium and tritium. Amongst them tritium can undergo beta-decay accompanied by release of a large amount of energy. Use this concept to find the radioactive element of hydrogen.

Complete answer:
The isotopes of the hydrogen are
$\left( i \right){\text{ }}{}_1{H^1}$ - Protium
$\left( {ii} \right){\text{ }}{}_1{H^2}$ - Deuterium
$\left( {iii} \right){\text{ }}{}_1{H^3}$ - Tritium
Now, $_1H^3$ is known as tritium and contains one proton and two neutrons in its nucleus (mass number = 3).
It is radioactive, decaying into helium-3 through beta-decay accompanied by a release of 18.6 keV of energy.
It has a half-life of 12.32 years.
Naturally occurring tritium is extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere with cosmic rays.
So this is the required answer.
Hence option (A) is the correct answer.

Note – The short life of tritium has also led to its classification as a highly radioactive element. Tritium does not emit any gamma ray at all. The neutrons in the tritium nucleus increases the attractive strong nuclear force when brought close to another atomic nucleus. As a result, tritium can more easily fuse with other light atoms, compared with the ability of ordinary hydrogen to do so.