Question

Across the lanthanide series, the basicity of the lanthanide hydroxides

• A. increases
• B. decreases
• C. first increases and then decreases
• D. first decreases and then increases

Hint:

Lanthanide hydroxides become less basic from La(OH)\(_3\) to Lu(OH)\(_3\) due to lanthanide contraction and increased covalent character.

Answer 1

The Correct Option is B

Step 1: Lanthanide contraction.
Across lanthanide series, atomic/ionic radius decreases due to poor shielding of \(4f\) electrons.
This is called lanthanide contraction.
Step 2: Effect on basicity.
As ionic size decreases, polarizing power increases.
So \(Ln^{3+}\) ions attract \(OH^-\) more strongly and form stronger \(Ln-O\) bonds.
Thus hydroxides become less ionic and less basic.
Step 3: Hence basicity decreases.
Final Answer: \[ \boxed{\text{decreases}} \]