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Which of the following facts is not true?

$\begin{array}{1 1}(a)\;\text{If }E^0_{Mn^+/M} \text{is -ve,}H^+\text{ will be reduced to }H_2\text{ by metal M}\\(b)\;\text{If }E^0_{Mn^+/M} \text{is +ve,}Mn^+\text{ will be reduced to }M\text{ by }H_2\\(c)\;\text{In a cell, }Mn^+/M\text{ assembly is attached to hydrogen half cell.To produce spontaneous cell reaction,metal M will act as negative electrode if the potential }Mn^+/M\text{ is negative.It will be serve as positive electrode,if }Mn^+/M\text {has a positive cell potential}\\(d)\;\text{Compounds of active metals (Zn,Na,Mg) are reducible by }H_2\text{ whereas those of noble metals(Cu,Ag,Au) are not reducible}\end{array}$

1 Answer

If a given metal ion has negative reduction potential,then $H^+$ will be reduced by metal.Conversely,if reduction potential is positive,metal be reduced by $H_2$.If metal ion with negative potential coupled with hydrogen electrode,the hydrogen half-cell should function as cathode,thus metal electrode will be negative half cell (anode).In aqueous solution containing $Zn^+,Na^+,Mg^{+2}$,the $H^+$ will get preferentially reduced while in aqueous solution of $Cu^{+2},Ag^+$ and $Au^{+3}$ these ions will be discharged ahead of $H^+$.
Hence (d) is the correct answer.
answered Feb 17, 2014 by sreemathi.v

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