Question

Why sodium get deposited on cathode not on anode ?

Answer 1

The redox couple Na+/Na has a very negative redox potential, meaning it is very hard to reduce and if reduced it very strongly tries to give its electron to something else. If there is nothing to accept the electrons but Na, as in the NaCl melt Alistair referred to, then you will get (liquid) Na metal. If it is in aqueous solution, the electrons go onto H+ and you get hydrogen gas. In fact if you were to reduce some sodium metal, what does sodium do when in contact with water? It reduces H+ to hydrogen gas in a reaction so spontaneous that the heat evolved ignites the hydrogen! And you are left with NaOH solution, the Na+ from oxidation of Na metal and the OH- from water as it dissociates to replace the leaving H+ ions.