Assertion (A): Transition metals form a large number of complex compounds.
Reason (R): Transition metal ions are comparatively small in size, have high ionic charges and have d orbitals available for bond formation.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are true and (R) is the correct explanation of (A).
In a complex compound the metal ion binds a number of anions or neutral molecules (ligands), for example [Fe(CN)6]3−, [Cu(NH3)4]2+ and [PtCl4]2−. Each ligand gives a pair of electrons to the metal ion.
Assertion (A): Transition metals form a large number of complex compounds. — True. Complex formation is one of the characteristic properties of transition metals, along with variable oxidation states and coloured ions.
Reason (R): Transition metal ions are comparatively small in size, have high ionic charges and have d orbitals available for bond formation. — True. These three features belong to the transition metal ions themselves.
Why R explains A?
Assertion (A) is about how readily transition metals form complexes; Reason (R) gives the features of their ions.
A small ion with a high charge attracts the ligands strongly, and its vacant d orbitals can accept the electron pairs the ligands donate. So R gives the cause of A.
NCERT (2026-27 edition):
4.3.11 Formation of Complex Compounds – “Complex compounds are those in which the metal ions bind a number of anions or neutral molecules giving complex species with characteristic properties. … The transition metals form a large number of complex compounds. This is due to the comparatively smaller sizes of the metal ions, their high ionic charges and the availability of d orbitals for bond formation.”