d-block elements form complex compounds, Give reason. 

Explanation

(i) Transition metal ions have smaller size and greater positive charge. Hence their polarizing power is high. Polarising power `= ("charge")/("size")`
  Due to high polarizing power, d-block metal ions can attract electrons of the ligands to form co ordinate bonds.
(ii) d-block metal ions have vacant d-orbitals that can overlap with the orbital of the ligands.