The sepence of filling electgron in sub-shells of element with few exception in d-block and f-block element is govemed by.Aufhau principal followed by Hand's rule and palli's ecxcited principal
a. The electron prefers to unter into sub-shell with lower `(n +1)` values
The energy for any sub-shell of an element other than hydrogen is preportioanal to the sum of principal quantum number (n) and angular momentum quantum number
b. If `(n + 1)` value is same for many sub-shell with lowest n value
c. i. Fulfiling sub-shell is more stable
ii. Half filled sub-shell is more stable less than half filed
Which pair of element follow rulke (c ) (ii) ?

Options

A. `Cr,Mo`
B. `Mo,Fe`
C. Cu,Ag`
D. `N,P`

Explanation

To solve the question regarding which pair of elements follows the rule that a half-filled subshell is more stable than a less than half-filled subshell, we can analyze the electronic configurations of the elements mentioned.

### Step-by-Step Solution:

1. **Understanding the Stability of Half-Filled and Fully Filled Subshells:**
- According to the stability rules, half-filled subshells (like d5) and fully filled subshells (like d10) are more stable due to symmetry and exchange energy.

2. **Identifying the Elements:**
- We need to consider the elements mentioned in the question: Chromium (Cr), Molybdenum (Mo), Iron (Fe), Copper (Cu), and Silver (Ag).

3. **Finding Electronic Configurations:**
- **Chromium (Cr)**:
- Atomic number: 24
- Electronic configuration: \( [Ar] 3d^5 4s^1 \) (3d is half-filled)
- **Molybdenum (Mo)**:
- Atomic number: 42
- Electronic configuration: \( [Kr] 4d^5 5s^1 \) (4d is half-filled)
- **Iron (Fe)**:
- Atomic number: 26
- Electronic configuration: \( [Ar] 3d^6 4s^2 \) (3d is not half-filled)
- **Copper (Cu)**:
- Atomic number: 29
- Electronic configuration: \( [Ar] 3d^{10} 4s^1 \) (3d is fully filled)
- **Silver (Ag)**:
- Atomic number: 47
- Electronic configuration: \( [Kr] 4d^{10} 5s^1 \) (4d is fully filled)

4. **Analyzing the Stability Rule (c ii):**
- The rule states that a half-filled subshell is more stable than a less than half-filled subshell.
- From the configurations:
- Chromium (Cr) and Molybdenum (Mo) both have half-filled d subshells.
- Iron (Fe) does not have a half-filled subshell.
- Copper (Cu) and Silver (Ag) have fully filled d subshells.

5. **Conclusion:**
- The pair of elements that follows the rule (c ii) is **Chromium (Cr)** and **Molybdenum (Mo)**, as both have half-filled d subshells.

### Final Answer:
The pair of elements that follow the rule (c ii) is **Chromium (Cr)** and **Molybdenum (Mo)**.