Read the passage given below and answer the following questions: 

The d-block consists of three series of elements: 3d, 4d and 5d series corresponding to the filling of 3d, 4d and 5d orbitals. All the transition elements exhibit metallic properties. Their melting points, boiling points and enthalpy of atomisation are high which are attributed to the involvement of both (n – 1)d and ns electrons resulting in strong interatomic bonding. Transition elements due to the involvement of (n–1)d electrons show properties like colour, variable oxidation states, exhibit paramagnetism, catalytic properties, interstitial compounds and complexes.