Two nuclei A and B are isotonic with mass numbers 15 and 16 respectively . If A contains 7 protons , then the number of protons in B would be

Options

A. 7
B. 8
C. 9
D. 10

Answer

To solve the problem, we need to understand the concept of isotonic nuclei. Isotonic nuclei have the same number of neutrons but different numbers of protons.

### Step-by-Step Solution:

1. **Identify the mass numbers and protons of nucleus A**:
- Nucleus A has a mass number \( A_A = 15 \).
- It contains \( Z_A = 7 \) protons.

2. **Calculate the number of neutrons in nucleus A**:
- The number of neutrons \( N_A \) can be calculated using the formula:
\[ N_A = A_A - Z_A \]
- Substituting the values:
\[ N_A = 15 - 7 = 8 \]

3. **Identify the mass number of nucleus B**:
- Nucleus B has a mass number \( A_B = 16 \).

4. **Since A and B are isotonic, the number of neutrons in B is the same as in A**:
- Therefore, \( N_B = N_A = 8 \).

5. **Calculate the number of protons in nucleus B**:
- The number of protons \( Z_B \) can be calculated using the formula:
\[ Z_B = A_B - N_B \]
- Substituting the values:
\[ Z_B = 16 - 8 = 8 \]

6. **Conclusion**:
- The number of protons in nucleus B is \( Z_B = 8 \).

### Final Answer:
The number of protons in nucleus B is **8**.

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