The element whose oxide will turn red litmus solution to blue will be:

Which of the following reactions will not occur? Why not? 

(a)$\underset{\left(\mathrm{solution}\right)}{\mathrm{Zinc} \mathrm{sulphate}}+\mathrm{Copper}\to \underset{\left(\mathrm{solution}\right)}{\mathrm{Copper} \mathrm{sulphate}}+\mathrm{Zinc}$

(b) $\underset{\left(\mathrm{solution}\right)}{\mathrm{Copper} \mathrm{sulphate}}+\mathrm{Iron}\to \underset{\left(\mathrm{solution}\right)}{\mathrm{Iron} \mathrm{sulphate}}+\mathrm{Copper}$