How many isotopes has hydrogen?

1. Analyze the question The question asks how many isotopes hydrogen has. Isotopes are atoms of the same element with the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers).

2. Explain the concept Hydrogen always has 1 proton. The common isotopes differ in their neutron count:

| Isotope | Name | Protons | Neutrons | Mass number | |---|---|---|---|---| | ¹H | Protium | 1 | 0 | 1 | | ²H | Deuterium | 1 | 1 | 2 | | ³H | Tritium | 1 | 2 | 3 |

3. Solution

• Protium (¹H) is the most abundant form, with no neutrons.
• Deuterium (²H or D) has 1 neutron. It is used to make "heavy water" (D₂O).
• Tritium (³H or T) has 2 neutrons. It is radioactive.

So the three naturally occurring isotopes of hydrogen are protium, deuterium, and tritium.

(Scientists have made heavier, extremely unstable hydrogen isotopes in laboratories, up to ⁷H. But at the WASSCE level, the expected answer is the three standard isotopes.)

4. Answer Hydrogen has 3 isotopes, which is option B.

5. Exam tip Remember "P-D-T": Protium, Deuterium, Tritium, with mass numbers 1, 2, 3. Their neutron counts are 0, 1, 2. Also keep in mind that isotopes have the same chemical properties (same electron arrangement) but different physical properties (such as mass and density).