Aluminium displaces hydrogen from acids, but copper does not . A galvanic cell prepared by combining $\mathrm{Cu}/{\mathrm{Cu}}^{2+}\text{ and }\mathrm{Al}/{\mathrm{Al}}^{3+}$has an emf of 2.0 V at 298K. If the potential of copper electrode is + 0.34V, that of Aluminium electrode is 

The given statement explains that Al is placed above Cu in E.C.S. hence it can reduce Cu (cathode) from its salt solution (reduction). Thus Al acts as a reducing agent(anode)
now, Given electrode potential of copper is 

$$\begin{gathered} E_{C{u}^{2+}/Cu}^o=+0.34V \\ {E}_{cell}^o\hspace{0.17em}= 2 V\hspace{0.17em} \end{gathered}$$

We know that 

$E_{cell}^o=E_{Cathode}^o-E_{anode}^o$

$$\begin{gathered} 2.0=0.34-E_{A{l}^{3+}/Al}^o \\ on solving \\ {E}_{A{l}^{3+}/Al}^o=-1.66V \end{gathered}$$