Given below are two statements:
Statement I: The decrease in first ionization enthalpy from B to Al is much larger than that from Al to Ga.
Statement II: The orbitals in Ga are completely filled.
In the light of the above statements, choose the most appropriate answer from the options given below
Statement I is incorrect but statement II is correct.
Both the statements I and II are correct
Statement I is correct but statement II is incorrect
Both the statements I and II are incorrect
Correct answer:A
Standard Method
Given: Two statements about the trend in first ionization enthalpy from B to Al and from Al to Ga.
Find: Which combination of statements is correct.
For Statement I, the drop in first ionization enthalpy from B to Al occurs because Al has an additional shell, so shielding increases and the outer electron is removed more easily.
For the comparison from Al to Ga, the decrease is not much larger in the same way because the filled electrons in Ga show poor shielding. As a result, the effective nuclear attraction on the outer electron remains relatively higher, so only a slight decrease in ionization enthalpy is observed.
Therefore, Statement I is incorrect.
For Statement II, Ga has completely filled orbitals. This is correct and helps explain the poor shielding effect mentioned above.
Therefore, Statement II is correct.
Hence, the correct option is A.
Assuming that ionization enthalpy must always decrease smoothly down a group is incorrect. Poor shielding by filled electrons can disturb the expected trend. Check electronic configuration before applying the simple down-the-group rule.
Ignoring the role of the filled subshell in Ga leads to the wrong conclusion. The electrons do not shield effectively, so the change from Al to Ga is smaller than a simple size argument suggests.
Confusing 'decrease exists' with 'decrease is much larger' is a conceptual error. Statement I is about the relative magnitude of two decreases, so the comparison must be evaluated carefully.
Get unlimited AI-adaptive practice, mastery tracking, and an AI tutor that explains every step — free to start.
