Answer
We can rank the electrons according to their ground-state energies:
$a \gt c \gt b$
Work Step by Step
In the ground state, $n=1$
We can write an expression for the ground-state energy of an electron in a potential well:
$E_1 = (\frac{h^2}{8m~L^2})~n^2 = \frac{h^2}{8m~L^2}$
As the width $L$ increases, the energy decreases.
We can rank the electrons according to their ground-state energies:
$a \gt c \gt b$
