how to caaculate n in nerst equation

The Nernst Equation allows us to calculate the voltage produced by any electrochemical cell given E^o values for its electrodes and the concentrations of reactants and products.

The general Nernst Equation: E = E^o -(RT/nF)lnQ 

      E^o = standard electrochemical cell potential (voltage) 
      R = ideal gas constant 
      T = temperature 
      n = moles of electrons 
      F = Faraday constant = 96,485 C mol^-1 
      Q = mass-action expression (approximated by the equilibrium expression)
 
At 25^oC the Nernst Equation is simplified to: E = E^o -(0.0592/n)logQ 
      E^o = standard electrochemical cell potential (voltage) 
      n = moles of electrons 
      Q = mass-action expression (approximated by the equilibrium expression)
 
For a system at equilibrium at 25^oC, E = 0 and the Nernst Equation is simplified to:
      E^o = (0.0592/n)logK 
      E^o = standard electrochemical cell potential (voltage) 
      n = moles of electrons 
      K = equilibrium expression