Question

Given below are two statements. Statement I: First ionisation enthalpy of Cr is greater than that of Mn. Statement II: Second and third ionisation enthalpies of Cr are less than that of Mn. In the light of above statements, choose the correct option.

• A. Both statement I and statement II are correct
• B. Both statement I and statement II are incorrect
• C. Statement I is correct but statement II is incorrect
• D. Statement I is incorrect but statement II is correct

Hint:

Ionisation enthalpies depend on the stability of the electron configuration, and Cr has a more stable configuration than Mn after the first ionisation.

Answer 1

The Correct Option is C

The question revolves around understanding the ionization enthalpy trends in the transition metals, specifically Chromium (Cr) and Manganese (Mn). Let's analyze both statements individually:

1. Statement I: First ionization enthalpy of Cr is greater than that of Mn.
   • The first ionization enthalpy refers to the energy required to remove the outermost electron from a neutral atom in the gaseous state.
   • The electron configuration of Chromium is \text{[Ar]} 4s^1 3d^5 and that of Manganese is \text{[Ar]} 4s^2 3d^5.
   • In Cr, the half-filled d-orbital (3d^5) provides extra stability, making it more difficult to remove the 4s electron, resulting in a higher ionization enthalpy compared to Mn.
   • Therefore, Statement I is correct.
2. Statement II: Second and third ionisation enthalpies of Cr are less than that of Mn.
   • The second ionization enthalpy refers to the energy required to remove an electron from a unipositive ion.
   • After the first ionization, Chromium becomes \text{Cr}^+ with electronic configuration \text{[Ar]} 3d^5, and Manganese becomes \text{Mn}^+ with electronic configuration \text{[Ar]} 3d^5 4s^1.
   • For the second electron removal, Manganese loses one of its d-electrons, making it less stable, resulting in a higher second ionization enthalpy for Mn than Cr.
   • The third ionization involves removing another electron from the already less stable configuration of Mn, while Cr maintains its half-filled stability longer.
   • Thus, the second and third ionization enthalpies of Mn are actually higher than those of Cr.
   • Therefore, Statement II is incorrect.

Based on the analysis above, the correct option is: Statement I is correct but Statement II is incorrect.