Two electrolytic cells containing silver nitrate solution and dilute sulphuric acid were connected in a series. A steady current of $2.5 \mathrm{A}$ was passed through them till $1.078 \mathrm{g}$ of silver was deposited $(\mathrm{Ag} = 107.8 \mathrm{g}/\mathrm{mol})$. What is the weight of oxygen gas liberated during the reaction?
 

How many moles of $\mathrm{Hg}$ will be produced by electrolysing $1.0 \mathrm{M} \mathrm{Hg}({\mathrm{NO}}_3{)}_2$ solution with a current of $2.00 \mathrm{A}$ for $3$ hours?

$\left[\mathrm{Hg}\right({\mathrm{NO}}_3{)}_2= 200.6 \mathrm{g}/\mathrm{mol}]$

Iron may be protected from rusting by coating with zinc or tin. By referring to the data given below, explain why zinc protects iron more effectively than tin? ${\mathrm{Zn}}^{2+}+ 2{\mathrm{e}}^{-} \to \mathrm{Zn}, {\mathrm{E}}^{°} = -0.76 \mathrm{V}; {\mathrm{Fe}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Fe}, \mathrm{E}°= - 0.44 \mathrm{V}; {\mathrm{Sn}}^{2+}+ 2{\mathrm{e}}^{-}\to \mathrm{Sn}, \mathrm{E}°=-0.14 \mathrm{V}$.

Why hydrogen is considered as a fuel resource for future?

What is the difference between primary and secondary cells? Differentiate using their applications also.