c
\(C{u^{ + 2}}\, + \,\,2{e^ - }\, \to \,\,Cu\,\,\,\,\,\,\,\,\,\,\,\,E_1^o \, = \,\,0.377\,\,volt,\,\,{n_1}\, = \,\,2\)

\(\because \,\,C{u^{ + 2}}\, + \,\,{e^ - }\, \to \,\,C{u^ + }\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{E^ o }\, = \,\,  \,\,0.153\,\,volt\)

\(\therefore \,\,C{u^ + }\, \to \,\,C{u^{ + 2}}\, + \,\,{e^ - }\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,E_2^o \,= \,- \,0.153\,volt,\,\,{n_2}\, = \,1\)

\(C{u^ + }\, + \,\,{e^ - }\, \to \,\,Cu\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,E_3^o \,\, = \,\,??,\,\,{n_3}\, = \,\,1\)

\(\therefore \,{\mkern 1mu} {\mkern 1mu} E_3^o{\mkern 1mu} {\mkern 1mu}  = \frac{{{\mkern 1mu} {n_1}E_1^o{\mkern 1mu}  + {\mkern 1mu} {\mkern 1mu} {n_2}E_2^o}}{{{n_3}}}\)

\( = \,\,\frac{{2\,\, \times \,\,0.337\,\, + \,\,1\,\, \times \,\,( - 0.153)}}{1}\)

\( = \,\,\,0.521\,\,volt\)