If standard reduction potential of four electrodes A, B, C, D are $+2.5\,\text{V}, +3.0\,\text{V}, -2.0\,\text{V}$ and $-1.5\,\text{V}$ respectively. When is the standard emf of cell maximum?

What happens in the oxidation number of Mn during working of dry cell.

For a certain redox reaction in galvanic cell $\text{X}_{(s)} + \text{Y}^{2+}_{(aq)} \longrightarrow \text{X}^{2+}_{(aq)} + \text{Y}_{(s)}$, $\text{E}^\circ$ cell is $0.0296\ \text{V}$ at $298\ \text{K}$. What is equilibrium constant of reaction?

Which of the following net cell reactions occurs in a galvanic cell containing cadmium electrode and standard hydrogen electrode?
$\text{E}^\circ_{(\text{Cd}^{2+}_{(aq)}|\text{Cd}_{(s)})} = -0.403\ \text{V}$.