Question

The correct order of ionic radii of Y³⁺, La³⁺, Eu³⁺ and Lu³⁺ is
(a) La³⁺ < Eu³⁺ < Lu³⁺ < Y³⁺
(b) Y³⁺ < La³⁺ < Eu³⁺ < Lu³⁺
(c) Y³⁺ < Lu³⁺ < Eu³⁺ < La³⁺
(d) Lu³⁺ < Eu³⁺ < La³⁺ < Y³⁺
(Atomic nos. Y =39, La = 57, Eu = 63, Lu = 71)

Answer 1

The correct order of ionic radii of Y³⁺, La³⁺, Eu³⁺ and Lu³⁺ is:

Y³⁺ < Lu³⁺ < Eu³⁺ < La³⁺

-Lutetium (Lu = 71) and Europium (Eu = 63) belongs to the lanthanide series.

- so they show lanthanide contraction

- due to this they are smaller in size than Lanthanum (La = 57)

- moreover, on going from left to rightin period, the ionic size decreases, so lanthanum is biggest, europium less than it and lutetium is the smallest among the three

- Yttrium (Y = 39) lies above lanthanum in the group, so it is bigger than it

-due to the above reasons, the correct order of ionic radii of given cations becomes:

Y³⁺ < Lu³⁺ < Eu³⁺ < La³⁺

- so the correct answer is (c)