Can you explain why the metal doesn't rust at b

(a)  (i) Zinc blende is mainly Zinc sulphide and in industry it is converted to ZnO by flames to burn off the sulphur as SO2 which is then used to make sulphuric acid.

(ii)   Reduction of ZnO to Zn:-

2ZnO + C = CO2 + 2Zn

(b) This is called sacrificial anodic protection.  The zinc ( which is more reactive than iron) when in contact with the oxygen in the air is oxidised and in the process loses its electrons. These travel  through the electrolyte to the iron. The electrons then reduce any iron oxide to iron: fe2+ + 2e  ---> Fe.