In electrolysis of 
when Pt electrode is taken then 
is liberated at cathode while with Hg cathode it forms sodium amalgam
at Hg than at Pt
ions is larger when Pt electrode is taken.
Text Solution
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When sodium chloride is dissolved in water, it ionises as 
. Water also dissociates as: 
During passing of electric current through this solution using platinum electrode, 
and 
ions move towards cathode. However, only 
ions are discharged more readily than 
ion because of their low discharge potential (In the electromotive series hydrogen is lower than sodium). These 
ions gain electrons and change into neutral atoms. At cathode 
and 
ions move towards anode. 
ions lose electrons and change into neutral atom. At anode, 
If mercury is used as cathode 
ions are not discharged at mercury cathode because mercury has a high hydrogen overvoltage. 
ions are discharged at the cathode in perference to 
ions, yielding sodium, which dissolves in mercury to form sodium amalgam. At cathode: 
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