Exams › JEE Advanced › Chemistry

Consider the following two statements about ionization enthalpy trends in Group 13: Statement I: The decrease in first ionization enthalpy going from B to Al is much larger than the decrease going from Al to Ga. Statement II: The 3d orbitals in gallium (Ga) are completely filled. Which of the following is the correct assessment of these statements?

1. Statement I is incorrect but Statement II is correct.
2. Both Statement I and Statement II are correct.
3. Statement I is correct but Statement II is incorrect.
4. Both Statement I and Statement II are incorrect.

Correct answer: Both Statement I and Statement II are correct.

Solution

Statement I is correct: IE1 drops sharply from B (~800 kJ/mol) to Al (~577 kJ/mol) but barely changes from Al to Ga (~579 kJ/mol). Statement II is correct: Ga has a completely filled 3d¹⁰ shell. The d electrons shield poorly, increasing effective nuclear charge in Ga and explaining why IE does not drop further from Al to Ga.

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