Which of the following isotopes of hydrogen is radioactive?

Options

A. `""_(1)^(1)H`
B. `""_( 1)^(2)H`
C. `""_(1)^(3)H`
D. none of these.

Answer

To determine which isotope of hydrogen is radioactive, we need to analyze the three isotopes of hydrogen: Protium, Deuterium, and Tritium.

### Step-by-Step Solution:

1. **Identify the Isotopes of Hydrogen**:
- Hydrogen has three isotopes:
- Protium (¹H) - 1 proton, 0 neutrons
- Deuterium (²H) - 1 proton, 1 neutron
- Tritium (³H) - 1 proton, 2 neutrons

2. **Check for Radioactivity**:
- Protium (¹H) is stable and does not undergo radioactive decay.
- Deuterium (²H) is also stable and does not undergo radioactive decay.
- Tritium (³H) is known to be radioactive. It has one proton and two neutrons and undergoes beta decay.

3. **Understand Tritium's Decay**:
- Tritium decays into Helium-3 (³He) by emitting a beta particle (an electron). This process is known as beta decay.

4. **Conclusion**:
- Among the three isotopes of hydrogen, Tritium (³H) is the only radioactive isotope.

### Final Answer:
The radioactive isotope of hydrogen is Tritium (³H).

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