Question

Ionization energy decreases as we move down the group. But moving down from the second to the third transition series ionization energy increases except for $Y$ to $La$. This is due to:

• A. lanthanide contraction
• B. change in the electronic configuration
• C. poor screening of d-electrons
• D. all of the above

Answer 1

The correct option is A lanthanide contraction

Due to Lanthanide contraction, the ionization energy increases from the second to the third transition series. Lanthanide contraction is due to the poor shielding of 4f electrons.