NEETChemistryClassification of Elements and Periodicity in Properties
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The first ionization enthalpy of Magnesium is greater than that of Aluminium, but the second ionization enthalpy of Magnesium is lower than that of Aluminium. Reason (R): The valence electron configuration of Mg is 3s² and that of Al is 3s² 3p¹ , whereas their univalent cations Mg ⁺ and Al ⁺ have 3
Options
- ABoth (A) and (R) are true but (R) is NOT the correct explanation of (A).
- BBoth (A) and (R) are true and (R) is the correct explanation of (A).
- C(A) is true but (R) is false.
- D(A) is false but (R) is true.
Correct answer
B. Both (A) and (R) are true and (R) is the correct explanation of (A).
Step-by-step solution
Assertion (A) is true: The first ionization enthalpy of Mg is greater than that of Al . However, the second ionization enthalpy of Mg is lower than that of Al . Reason (R) is true and correctly explains (A): The first electron in Mg is removed from a fully filled and more penetrating 3s orbital ( 3s² ), requiring more energy than the removal of the 3p¹ electron in Al . For the second ionization, the electron is removed from Mg ⁺ ( 3s¹ ) and Al ⁺ ( 3s² ). Because Al ⁺ has acquired a stable fully filled 3s² configura