Hydrogen and deuterium differ in:

Options

A. Reactivity with oxygen
B. Reactivity with chlorine
C. Melting point
D. Reducing action

Answer

To solve the question regarding the differences between hydrogen and deuterium, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Isotopes**:
- Hydrogen (H) and Deuterium (D) are both isotopes of the element hydrogen. Isotopes have the same atomic number but different mass numbers.

2. **Atomic Numbers**:
- Both hydrogen and deuterium have the same atomic number, which is 1. This means they both have one proton in their nucleus.

3. **Mass Numbers**:
- The mass number of hydrogen is 1 (it has one proton and no neutrons).
- The mass number of deuterium is 2 (it has one proton and one neutron). This difference in mass is what distinguishes the two isotopes.

4. **Chemical Properties**:
- Since hydrogen and deuterium are isotopes of the same element, they exhibit similar chemical properties. This means they react in the same way with other substances, such as oxygen and chlorine.

5. **Physical Properties**:
- The physical properties of hydrogen and deuterium differ due to the difference in mass. For example, they have different melting points and boiling points. Deuterium has a higher melting point and boiling point compared to hydrogen.

6. **Conclusion**:
- In summary, hydrogen and deuterium differ in their physical properties (like melting and boiling points) but have the same chemical properties.

### Final Answer:
Hydrogen and deuterium differ in their physical properties, such as melting point and boiling point, while their chemical properties remain the same.

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