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

Concept: Electronic configurations: \[ Cr: [Ar]\,3d^5\,4s^1 \] \[ Mn: [Ar]\,3d^5\,4s^2 \] Half-filled \(3d^5\) configuration is particularly stable. Step 1: {First ionisation enthalpy} Removing one electron: \[ Cr \rightarrow [Ar]3d^5 \] This produces a stable half-filled configuration. Thus ionisation is relatively easier. Hence \[ \Delta_iH_1(Mn)>\Delta_iH_1(Cr) \] So statement A is correct. Step 2: {Second ionisation enthalpy} After first ionisation: \[ Cr^+ : [Ar]3d^5 \] Removing another electron breaks the stable half-filled configuration. Thus second ionisation energy becomes high. For Mn: \[ Mn^+ : [Ar]3d^5\,4s^1 \] Second ionisation removes the \(4s\) electron easily. Thus \[ \Delta_iH_2(Cr)>\Delta_iH_2(Mn) \] Hence statement D is correct. Therefore correct statements are: \[ A \text{ and } D \]