Answer
$S = 0$
Work Step by Step
The entropy is given by the Boltzmann's entropy equation
$S = k ln( W)$ where W is the multiplicity.
To find the least entropy, we use the least multiplicity from$ (a)$ which is $ 1$ and $k = 1.38 \times 10^{-23}$ So,
$S = 1.38 \times 10^{-23} ln( 1.0 )$
$S = 0$
