Which of the following is a light element indicating radioactivity

Correct option is C

The correct answer is (c) Tritium

Explanation:
• Tritium is an exceptionally light radioactive isotope of hydrogen with a distinct atomic mass of 3 (containing one proton and two neutrons).
• Because its nucleus is unstable, tritium actively decays by emitting low-energy beta particles and has a half-life of approximately 12.3 years.

Information Booster:
• Due to its beta-emitting properties, tritium is heavily used in self-illuminating devices (like radioluminescent watch dials and emergency exit signs).
• It is also a critical component fuel in nuclear fusion reactions, commonly paired with deuterium.

Additional Knowledge:
Hydrogen (Option a)
• Standard hydrogen (Protium) has one proton and zero neutrons, and its nucleus is entirely stable and non-radioactive.
Deuteron (Option b)
• A deuteron is the nucleus of Deuterium (one proton, one neutron). Deuterium is a stable, non-radioactive heavy isotope of hydrogen.
Helium (Option d)
• Standard Helium-4 is a highly stable, inert noble gas, famously non-radioactive (it is actually the end-product of alpha decay).
None of the above/More than one of the above (Option e)
• Incorrect, as tritium clearly represents a light radioactive element.

So the correct answer is (c)