Question

The catalytic activity of transition metals and their compounds is ascribed mainly to :

• A. their unfilled d-orbitals
• B. their ability of adopt variable oxidation states
• C. their chemical reactivity
• D. their magnetic behaviour

Answer 1

The correct option is B their ability of adopt variable oxidation states

The transition metals and their compounds are known for their catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. Vanadium(V) oxide (in Contact Process), finely divided iron (in Haber’s Process), and nickel (in Catalytic Hydrogenation) are some of the examples.
Also because the transition metal ions can change their oxidation states, they become more effective as catalysts. For example, iron(III) catalyses the reaction between iodide and persulphate ions. $2I^{–}+S_2{O}_8^{2–}\to I_2+2S{O}_4^{2–}$
An explanation of this catalytic action can be given as:
$2F{e}^{3+}+2I^{–}\to 2F{e}^{2+}+I_2$$2F{e}^{2+}+S_2{O}_8^{2–}\to 2F{e}^{3+}+2S{O}_4^{2–}$