Describe the transition elements as metals that: (a) have high densities (b) have high melting points (c) have variable oxidation numbers (d) form coloured compounds (e) often act as catalysts as elements and in compounds

State the typical conditions for the conversion of sulfur dioxide to sulfur trioxide in the Contact process as 450°C, 200 kPa/2 atm and a vanadium(V) oxide catalyst