A) Hg is more inert than Pt
B) more voltage is required to reduce \[{{\text{H}}^{\text{+}}}\]at Hg than at Pt
C) Na is dissolved in Hg while it does not dissolved in Pt
D) concentration of \[{{\text{H}}^{\text{+}}}\]ions is larger when Pt electrode is taken
Correct Answer: B
Solution :
Sodium chloride in water dissociates as \[NaClN{{a}^{+}}+C{{l}^{-}}\] \[{{H}_{2}}O{{H}^{+}}+O{{H}^{-}}\] When electric current is passed through this solution using platinum electrode, \[\text{N}{{\text{a}}^{\text{+}}}\]and \[{{\text{H}}^{\text{+}}}\]move towards cathode, whereas \[\text{C}{{\text{l}}^{-}}\]and \[\text{O}{{\text{H}}^{-}}\]ions move towards anode. At cathode \[{{H}^{+}}+{{e}^{-}}\xrightarrow{{}}H\] \[H+H\xrightarrow{{}}{{H}_{2}}\] At anode \[C{{l}^{-}}-{{e}^{-}}\xrightarrow{\,}\,Cl\] \[Cl+Cl\xrightarrow{{}}C{{l}_{2}}\] If mercury is used as cathode, \[{{\text{H}}^{\text{+}}}\]ions are not discharged at mercury cathode because mercury has a high hydrogen over voltage. \[\text{N}{{\text{a}}^{+}}\]ions are discharged at cathode in preference of ions yielding sodium, which dissolves in mercury to form sodium amalgam.
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