Answer
$\Delta S = 0$. Entropy is unchanged.
Work Step by Step
When gas is confined in an insulated cylinder, we assume that the heat transfer is zero due to the insulation.
In an adiabatic process, only volume changes and no heat is transferred.
$\Delta S = \frac{dQ}{T}$
Setting 0 into the entropy equation
$\Delta S = \frac{0}{T}$
$\Delta S = 0$
