Why do the transition elements form complexes?

How do the transition elements form pi- complexes ?

Why do the transition elements form coloured compounds?

Transition elements form complexes due to

Why do transitional elements form complex compounds ?

Why transition elements form complexes ? (OR) why do d-block elements form complexes ?

Give two reasos why transition elements can form complexes.

Why do transition elements from complex compounds? Name the elements which exhibit highest oxidation state.