Element P has 5 electrons in its L shell while Q element has 5 electrons in its M shell. Which of the following statements is correct regarding elements P and Q?

Options

A. Both elements have valency equal to 5 only.
B. Both elements have the same mass number.
C. Atomic number of element P is 7 and that of element Q is 15.
D. Both elements show valency equal to 3 only

Explanation

To determine which statement is correct regarding elements P and Q, we need to analyze their electronic configurations and atomic numbers based on the information provided.

### Step-by-Step Solution:

1. **Identify the Shells and Electrons:**
- Element P has 5 electrons in its L shell.
- Element Q has 5 electrons in its M shell.

2. **Determine the Electronic Configuration:**
- For element P:
- The K shell can hold 2 electrons, and the L shell can hold 8 electrons.
- Since P has 5 electrons in the L shell, the electronic configuration of P is:
- K shell: 2 electrons
- L shell: 5 electrons
- Thus, the electronic configuration of P is **2, 5**.

- For element Q:
- The K shell can hold 2 electrons, and the L shell can hold 8 electrons.
- Since Q has 5 electrons in the M shell, the electronic configuration of Q is:
- K shell: 2 electrons
- L shell: 8 electrons (fully filled)
- M shell: 5 electrons
- Thus, the electronic configuration of Q is **2, 8, 5**.

3. **Calculate the Atomic Numbers:**
- The atomic number is equal to the number of electrons in a neutral atom.
- For element P:
- Total electrons = 2 (K) + 5 (L) = **7**. Therefore, the atomic number of P is **7**.
- For element Q:
- Total electrons = 2 (K) + 8 (L) + 5 (M) = **15**. Therefore, the atomic number of Q is **15**.

4. **Determine the Valency:**
- Valency is determined by how many electrons an element needs to gain, lose, or share to complete its outer shell.
- For element P (7 electrons):
- It can gain 1 electron to complete its octet (8 electrons) or lose 5 electrons. Thus, the valency of P can be **1 or 5**.
- For element Q (15 electrons):
- It can gain 3 electrons to complete its octet (18 electrons) or lose 5 electrons. Thus, the valency of Q can be **3 or 5**.

5. **Evaluate the Given Statements:**
- **Statement A:** Both elements have valency equal to 5. (Incorrect, as P can have a valency of 1 or 5, and Q can have a valency of 3 or 5.)
- **Statement B:** Both elements have the same mass number. (Incorrect, as mass numbers will differ due to different atomic numbers.)
- **Statement C:** The atomic number of element P is 7 and that of element Q is 15. (Correct, as calculated.)
- **Statement D:** Both elements show valency equal to 3 only. (Incorrect, as both can have different valencies.)

### Conclusion:
The correct statement regarding elements P and Q is **Statement C**: The atomic number of element P is 7 and that of element Q is 15.

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