Question

Given below are two statements: Statement (I): The first ionisation enthalpy of the elements Na, Mg, Cl and Ar follows the order \[ Na>Mg>Cl>Ar \] Statement (II): Among Ca, Al, Fe and B, the third ionisation enthalpy is very high for Ca. In the light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Ionisation enthalpy generally increases across a period due to increased effective nuclear charge and decreased atomic radius. Sudden jumps in successive ionisation energies occur when an electron is removed from a stable noble gas configuration.
Step 2: Detailed Explanation:
1. Analysis of Statement (I):
The elements Na, Mg, Cl, and Ar belong to the same period (3rd period).
Moving left to right in a period, the effective nuclear charge increases, and the atomic size decreases.
Consequently, the energy required to remove an electron (IE1) increases.
Correct order of IE1: \(Na<Mg<Cl<Ar\).
The statement gives the reverse order (\(Na>Mg>Cl>Ar\)).
Therefore, Statement (I) is False.

2. Analysis of Statement (II):
Third ionisation enthalpy (\(IE_3\)) is the energy to remove an electron from a \(M^{2+}\) ion.
Electronic configuration of Calcium (Ca): \([Ar] 4s^2\).
\(Ca^+\): \([Ar] 4s^1\).
\(Ca^{2+}\): \([Ar]\) (Noble gas configuration).
Removing the third electron from \(Ca^{2+}\) involves breaking the exceptionally stable noble gas core of Argon.
This results in a very high value for \(IE_3\) for Calcium.
For Al, Fe, and B, the third electron removal does not involve breaking a noble gas core (e.g., Al becomes noble gas after \(IE_3\)).
Therefore, Statement (II) is True.
Step 3: Final Answer:
Statement I is false but Statement II is true.