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. (a)7
B. (b)8
C. (c)9
D. 10

Answer

To solve the problem, we need to determine the number of protons in nucleus B, given that nuclei A and B are isotonic and have mass numbers of 15 and 16, respectively. We also know that nucleus A contains 7 protons.

### Step-by-Step Solution:

1. **Understand the Concept of Isotonic Nuclei**:
- Isotonic nuclei have the same number of neutrons but different numbers of protons and mass numbers.

2. **Identify the Given Information**:
- Mass number of nucleus A (A) = 15
- Mass number of nucleus B (B) = 16
- Number of protons in nucleus A (Z_A) = 7

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

4. **Determine the Number of Neutrons in Nucleus B**:
- Since nuclei A and B are isotonic, they have the same number of neutrons:
\[ N_B = N_A = 8 \]

5. **Calculate the Number of Protons in Nucleus B**:
- The mass number of nucleus B (A_B) is given as 16. We can find the number of protons (Z_B) in nucleus B using the formula:
\[ A_B = Z_B + N_B \]
- Rearranging the formula gives:
\[ Z_B = A_B - N_B \]
- Substituting the values:
\[ Z_B = 16 - 8 = 8 \]

6. **Conclusion**:
- The number of protons in nucleus B is 8.

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

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