Assertion : `""_(14)Si^(30),""_(15)P^(31) and ""_(16)S^(32)` are a group of isotones.
Reason : Isotones are atoms of different elements having different mass numbers and atomic numbers but same number of neutrons in their nuclei.

Options

A. If both the assertion and reason are true statement and reason is correct explanation of the assertion .
B. If both the assertion and reason are true statement but reason is not a correct explanation of the assertion .
C. If the assertion is true but the reason is a false statement.
D. If both assertion and reason are false statements.

Explanation

To solve the question, we need to analyze the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
The assertion states that `""_(14)Si^(30),""_(15)P^(31) and ""_(16)S^(32)` are a group of isotones.

2. **Definition of Isotones**:
Isotones are defined as atoms of different elements that have the same number of neutrons in their nuclei, but different mass numbers and atomic numbers.

3. **Calculating Neutrons for Each Element**:
- For Silicon (Si):
- Atomic number (Z) = 14
- Mass number (A) = 30
- Number of Neutrons = A - Z = 30 - 14 = 16
- For Phosphorus (P):
- Atomic number (Z) = 15
- Mass number (A) = 31
- Number of Neutrons = A - Z = 31 - 15 = 16
- For Sulfur (S):
- Atomic number (Z) = 16
- Mass number (A) = 32
- Number of Neutrons = A - Z = 32 - 16 = 16

4. **Comparison of Neutron Counts**:
- All three elements (Si, P, S) have the same number of neutrons, which is 16.

5. **Conclusion about the Assertion**:
Since all three elements have the same number of neutrons, the assertion that they are a group of isotones is correct.

6. **Understanding the Reason**:
The reason states that isotones are atoms of different elements having different mass numbers and atomic numbers but the same number of neutrons in their nuclei. This definition is accurate.

7. **Conclusion about the Reason**:
The reason correctly explains the assertion.

8. **Final Evaluation**:
Both the assertion and the reason are correct, and the reason supports the assertion. Therefore, the correct answer is A (both assertion and reason are correct).