A brief information about two atoms `X` and `Y` is given :
`X` : Atomic number `= 7`, Mass number `= 14`
`Y` : Atomic number `= 7`, Mass number `= 15`
Which of the following is correct about these two atoms ?

Options

A. Electronic configuration of `X` is `2,8,4` while that of `Y` is `2, 8, 5`.
B. Both `X` and `Y` contain `7` neutrons.
C. `X` has `2` electron shells while `Y` has `3` electron shells.
D. Both `X` and `Y` have `5` valence electrons.

Explanation

To analyze the information given about the two atoms `X` and `Y`, we need to determine their atomic structure based on their atomic and mass numbers.

### Step-by-Step Solution:

1. **Identify the Atomic Number and Mass Number:**
- For atom `X`:
- Atomic Number (Z) = 7
- Mass Number (A) = 14
- For atom `Y`:
- Atomic Number (Z) = 7
- Mass Number (A) = 15

2. **Determine the Number of Protons:**
- The atomic number represents the number of protons in an atom.
- Therefore, both `X` and `Y` have:
- Protons in `X` = 7
- Protons in `Y` = 7

3. **Determine the Number of Neutrons:**
- The number of neutrons can be calculated using the formula:
\[ \text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number} \]
- For atom `X`:
\[ \text{Neutrons in } X = 14 - 7 = 7 \]
- For atom `Y`:
\[ \text{Neutrons in } Y = 15 - 7 = 8 \]

4. **Determine the Number of Electrons:**
- In a neutral atom, the number of electrons is equal to the number of protons.
- Therefore, both `X` and `Y` have:
- Electrons in `X` = 7
- Electrons in `Y` = 7

5. **Determine the Electron Configuration:**
- The electron configuration can be determined based on the number of electrons:
- For `X` (7 electrons):
- The configuration is 2 electrons in the first shell and 5 in the second shell (2, 5).
- For `Y` (7 electrons):
- The configuration is also 2 electrons in the first shell and 5 in the second shell (2, 5).

6. **Determine the Valence Electrons:**
- Valence electrons are the electrons in the outermost shell.
- For both `X` and `Y`, the outermost shell has 5 electrons.

### Conclusion:
- Both atoms `X` and `Y` have the same number of protons (7) and the same electron configuration (2, 5). However, they differ in the number of neutrons (7 for `X` and 8 for `Y`).
- Therefore, the correct statement is: **Both `X` and `Y` have 5 valence electrons.**