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JEE MainChemistryClassification of Elements and Periodicity in Properties

Given below are two statements: Statement I: The first ionization enthalpy of Thallium (Tl) is greater than that of Aluminum (Al). Statement II: The atomic radius of Gallium (Ga) is strictly less than that of Aluminum (Al). In the light of the above statements, choose the most appropriate answer from the options given below:

Options

  1. ABoth Statement I and Statement II are incorrect.
  2. BBoth Statement I and Statement II are correct.
  3. CStatement I is correct but Statement II is incorrect.
  4. DStatement I is incorrect but Statement II is correct.

Correct answer

B. Both Statement I and Statement II are correct.

Step-by-step solution

Statement I is correct: Thallium (Group 13, Period 6) contains 4f and 5d electrons which shield the nucleus very poorly. This leads to a significant increase in the effective nuclear charge (lanthanide contraction effect), making the first ionization enthalpy of Tl higher than that of Al. The overall order of first ionization enthalpy for Group 13 is B > Tl > Ga > Al > In. Statement II is correct: Gallium (Period 4) contains 3d electrons that offer poor shielding (scandide contraction). This causes its valence elec

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