d- and f-Block Elements · Question 76

Which of the following statements is not correct?

1. La(OH)3 is less basic than Lu(OH)3.
2. In lanthanide series ionic radius of Ln3+ ion decreases.
3. La is actually an element of transition series rather than lanthanides.
4. Atomic radii of Zr and Hf are nearly the same because of lanthanide contraction.

Answer

(1) La(OH)3 is less basic than Lu(OH)3.

Solution

(1) Not correct: due to lanthanoid contraction the size of Ln3+ decreases from La to Lu, so the covalent character of Ln(OH)3 increases and basic strength decreases. Hence La(OH)3 is the most basic and Lu(OH)3 the least basic.

(2) Correct: the ionic radius of Ln3+ decreases steadily along the series (lanthanoid contraction).

(3) Correct: La ([Xe]5d1 6s2) has no 4f electron and resembles the group 3 transition elements.

(4) Correct: as per NCERT, because of lanthanoid contraction Zr (160 pm) and Hf (159 pm) have almost identical radii.

Answer: (1)