In Which of the Following Cases Must $\varepsilon$ Be Equal to Zero?
A)In Any Cell at Equilibrium

In which of the following cases must $\varepsilon$ be equal to zero?

A) In any cell at equilibrium.
B) In a concentration cell.
C) ( $\varepsilon$ ) can never be equal to zero.
D) Choices A and B are both correct.
E) None of these.