Which of the following statements are correct? I. P is having least negative electron gain enthalpy among P , S , Cl , and F II. In Eu , Yb Lanthanoid contraction is not observed III. Ce ( OH )₃ is most basic among lanthanoid hydroxides IV. The radii of Na and Na ⁺ are 95 pm , 186 pm respectively

Step-by-step solution

Europium ( Eu )=[ Xe ] 4 f ^7 5 ~d ^0 6 ~s ^2, 185 pm Ytterbium ( Yb )=[ Xe ] 4 f ¹⁴ 5 ~d ^0 6 ~s ^2, 170 pm In these two elements, the atomic radii do not show expected decrease due to lanthanoid contraction but instead show an increased value. This is due to an electron entering into the 4 f -orbital(inner shell) and giving rise to very stable half-filled and fullyfilled configurations that results in greater screening of the valence electrons (higher screening constant ) Thus, Statement II is correct. The value