What is the oxidation number of underlined species in $\mathrm{PF}_6^{-}$and $\mathrm{V}_2 \mathrm{O}_7^{-4}$ ions respectively?

Which among the following species is reduced by tin easily?

What is the number of moles of electrons gained by one mole oxidizing agent in following redox reaction?

$$\mathrm{Zn_{(s)}+2HCl_{(aq)}}$$ $$\longrightarrow$$ $$\mathrm{ZnCl_2+H_2}$$

Which from following elements exhibits usual tendency to undergo reduction?