$(a)$ Transition metals can act as catalysts because these can change their oxidation state. How does $Fe(III)$ catalyse the reaction between iodide and persulphate ions ?
$(b)$ Mention any three processes where transition metals act as catalysts.
$(a)$ Reaction between iodide and persulphate ions is given by $2 \mathrm{I}^{-}+\mathrm{S}_{2} \mathrm{O}_{8}^{2-} \stackrel{\mathrm{Fe}(\mathrm{III})}{\longrightarrow} \mathrm{I}_{2}+2 \mathrm{SO}_{4}^{2-}$
Mechanism :
$(i)$ $2 \mathrm{Fe}^{3+}+2 \mathrm{I}^{-} \rightarrow 2 \mathrm{Fe}^{2+}+\mathrm{I}_{2}$
$(ii)$ $2 \mathrm{Fe}^{2+}+2 \mathrm{~S}_{2} \mathrm{O}_{8}^{2-} \rightarrow 2 \mathrm{Fe}^{3+}+2 \mathrm{SO}_{4}^{2-}$
$(b)$ $(i)$ Contact process : $\mathrm{V}_{2} \mathrm{O}_{5}$
$(ii)$ Haber's process : Finely divided : Fe
$(iii)$ Decomposition of $\mathrm{KClO}_{3}: \mathrm{MnO}_{2}$
Which metal is present in brass, bronze and German silver
While filling up of electrons in the atomic orbitals, the $4 s$ orbital is filled before the $3 d$ orbital but reverse happens during the ionisation of the atom. Explain why?
Which of the following transitional metal has lowest boiling point (B.P.)
Most stable cation in aqueous medium is
Which of the following compounds is metallic and ferromagnetic ?