The transition metals generally form complex compounds due to:

(A) Variable oxidation states

(B) High ionic charges

(C) Smaller size of metal ion

(D) Metallic conductivity

(E) Availability of d-orbitals

Choose the correct answer from the options given below:

(B), (C), and (E) only

The correct answer is option 4. (B), (C), and (E) only.

Let us reassess the options:

(B) High ionic charges: Transition metals often form complex compounds due to their high ionic charges. These high charges make them capable of attracting and binding to negatively charged ligands, forming coordination complexes.

(C) Smaller size of metal ion: The smaller size of transition metal ions allows them to form close interactions with ligands, facilitating the formation of complex compounds.

(E) Availability of d-orbitals: The availability of d-orbitals in transition metals is crucial for the formation of complex compounds. These d-orbitals can accept electron pairs from ligands, leading to the coordination of ligands around the metal ion.

While variable oxidation states (option A) are indeed a characteristic of transition metals, they are not directly related to the formation of complex compounds.

Similarly, metallic conductivity (option D) is a property of metals but is not directly associated with the formation of complex compounds.

Therefore, upon reassessment, the correct answer is indeed: (4) (B), (C), and (E) only.

These options accurately represent the factors that contribute to the formation of complex compounds by transition metals.