Chemistry - f-block Question with Solution | TestHub

Option A is correct. Most lanthanoids react with dilute acids to liberate H₂ gas, as they are electropositive metals.

Option B is incorrect. Sm³⁺ is colored, but La³⁺ , Gd³⁺ and Lu³⁺ are colorless.

Option C is incorrect. Nb and Ta have similar sizes due to lanthanoid contraction, caused by poor shielding of 4f electrons, not 5f.

Option D is incorrect. Ce(IV) is an oxidizing agent, but its solution, like Ce(SO₄)₂, is yellow/orange, not colorless.