The correct order of the first ionization enthalpy is
- Al > Ga > Tl
- Ga > Al > B
- B > Al > Ga
- Tl > Ga > Al
The Correct Option is D
Solution and Explanation
(i) Due to the lanthanide contraction, thallium (Tl) has a higher first ionization enthalpy compared to gallium (Ga) and aluminum (Al). This is because the contraction results in a higher effective nuclear charge, which increases the ionization energy.
(ii) Similarly, the scandide contraction causes gallium to have a higher ionization energy than aluminum due to a similar increase in effective nuclear charge, making electrons harder to remove.
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