Question

The correct order of first \((\Delta_iH_1)\) and second \((\Delta_iH_2)\) ionisation enthalpy values of Cr and Mn are:}

• [A.] \( \Delta_iH_1: Cr>Mn \)
• [B.] \( \Delta_iH_2: Cr>Mn \)
• [C.] \( \Delta_iH_1: Mn>Cr \)
• [D.] \( \Delta_iH_2: Mn>Cr \)

Choose the correct answer.

• A. A and B only
• B. B and C only
• C. A and D only
• D. C and D only

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to compare the energy required to remove the first and second electrons from Chromium (Cr) and Manganese (Mn).
Step 2: Key Formula or Approach:
Write electronic configurations:
- Cr: \([\text{Ar}] 3d^5 4s^1\)
- Mn: \([\text{Ar}] 3d^5 4s^2\)
Step 3: Detailed Explanation:
1. First Ionization (\(\Delta_i H_1\)): Mn has a stable fully filled \(4s^2\) subshell. Removing an electron from Mn is harder than from the \(4s^1\) of Cr. Thus, \(Mn>Cr\). (Statement C is correct).
2. Second Ionization (\(\Delta_i H_2\)):
- \(\text{Cr}^{+}\) is \([\text{Ar}] 3d^5\) (very stable exactly half-filled configuration).
- \(\text{Mn}^{+}\) is \([\text{Ar}] 3d^5 4s^1\).
Removing the second electron from Cr means breaking the stable half-filled \(d^5\) shell, which requires much higher energy. Thus, \(Cr>Mn\). (Statement B is correct).
Step 4: Final Answer:
Both B and C are correct comparisons.