What does the negative sign in the expression $E_{Zn^{2+}|Zn}^o = -0.76 \ V$ mean?

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

The standard $E^{\circ}_{red}$ values of $A, B$ and $C$ are $+0.68 \ V, -2.54 \ V$ and $-0.50 \ V$ respectively. The order of their reducing power is:

Given:
$E^o_{Cr^{3+}/Cr} = -0.74 \ V$,$E^o_{MnO_4^-/Mn^{2+}} = 1.51 \ V$
$E^o_{Cr_2O_7^{2-}/Cr^{3+}} = 1.33 \ V$,$E^o_{Cl_2/Cl^{-}} = 1.36 \ V$
Based on the data given above,the strongest oxidising agent will be:

Given the electrode potentials:
$Fe^{3+} + e^- \to Fe^{2+}; E^o = 0.771 \ V$
$I_2 + 2e^- \to 2I^{-}; E^o = 0.536 \ V$
The $E^o_{\text{cell}}$ for the cell reaction $2Fe^{3+} + 2I^{-} \to 2Fe^{2+} + I_2$ is:

What is the standard electrode potential of a Daniell cell (in $V$)?