Which of the following pairs are isotopes

Options

A. oxygen and ozone
B. ice and steam
C. nitric oxide and nitrogen dioxid
D. hydrogen and deuteriu

Answer

To determine which pairs are isotopes, we need to understand the definition of isotopes. Isotopes are atoms of the same element that have the same atomic number (number of protons) but different mass numbers (total number of protons and neutrons).

### Step-by-Step Solution:

1. **Identify the Definition of Isotopes:**
- Isotopes are species that have the same atomic number but different mass numbers.

2. **Examine the Given Pairs:**
- We need to analyze the pairs provided in the question to see if they fit the definition of isotopes.

3. **Check Each Pair:**
- **Pair 1: Hydrogen (1H1) and Deuterium (2H1)**
- Both have the same atomic number (1) but different mass numbers (1 for hydrogen and 2 for deuterium).
- **Conclusion:** This pair is isotopes.

- **Pair 2: Oxygen (O2) and Ozone (O3)**
- These are different molecules (O2 is diatomic oxygen and O3 is ozone) and do not have the same atomic number or mass number.
- **Conclusion:** This pair is not isotopes.

- **Pair 3: Ice and Steam**
- Both are different states of water (H2O) but represent the same molecule and do not have different mass numbers.
- **Conclusion:** This pair is not isotopes.

- **Pair 4: Nitric Oxide (NO) and Nitrogen Dioxide (NO2)**
- These are different compounds of nitrogen and do not have the same atomic number or mass number.
- **Conclusion:** This pair is not isotopes.

4. **Final Answer:**
- The only pair that qualifies as isotopes is **Hydrogen (1H1) and Deuterium (2H1)**.

### Conclusion:
The correct answer is **option 4: Hydrogen and Deuterium**.