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JEE MainChemistryClassification 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 Gallium is marginally higher than that of Aluminum. Reason (R): The presence of 10 d-electrons in Gallium offers poor shielding effect for the valence electrons. In the light of the above statements, choose the correct answer from the options given below:

Options

  1. A(A) is false but (R) is true
  2. BBoth (A) and (R) are true but (R) is not the correct explanation of (A)
  3. CBoth (A) and (R) are true and (R) is the correct explanation of (A)
  4. D(A) is true but (R) is false

Correct answer

C. Both (A) and (R) are true and (R) is the correct explanation of (A)

Step-by-step solution

Normally, ionization enthalpy decreases down a group. However, Gallium follows immediately after the 3 d transition series. The 10 d-electrons in Ga provide poor shielding against the increased nuclear charge, leading to a higher effective nuclear charge on the valence electrons. This makes the ionization enthalpy of Ga slightly higher than Al. Thus, both A and R are true, and R is the correct explanation. Answer: Both (A) and (R) are true and (R) is the correct explanation of (A)

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