The total number of $$\mathrm{Mn}=\mathrm{O}$$ bonds in $$\mathrm{Mn}_{2} \mathrm{O}_{7}$$ is __________.

The dark purple colour of $$\mathrm{KMnO}_{4}$$ disappears in the titration with oxalic acid in acidic medium. The overall change in the oxidation number of manganese in the reaction is :

The electronic configuration of Pt (atomic number 78) is :

Which one of the lanthanoids given below is the most stable in divalent form?