Assertion: Toxic metal ions are removed by the chelating ligands.

Reason: Chelate complexes tend to be more stable.

The correct option is B

Assertion and reason both are true, reason is correct explanation of assertion.

Analysing the assertion

When a solution of chelating ligands is added to a solution containing toxic metals, the ligands chelate the metal ions by the formation of a stable cyclic complex.
Thus, toxic metal ions are removed by chelating ligands.

Example: EDTA (hexadentate ligand) forms a stable metal chelate and is used to remove toxic metal ions.

So, the assertion is a correct statement.

Analysing the reason

Chelating ligands form stable cyclic complexes with metal ions. Thus, the chelate complexes tend to be more stable. So, the reason is also a correct statement.

Hence, both the assertion and the reason are correct statements, and the reason is the correct explanation for the assertion.

So, option (A) is the correct answer.