Question

The correct order of the first ionization enthalpy is

• A. Al > Ga > Tl
• B. Ga > Al > B
• C. B > Al > Ga
• D. Tl > Ga > Al

Answer 1

The Correct Option is D

(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.