An equal amount of hydrogen gas is dissolved in a 1L vessel and a 2L vessel, both filled with water. Which vessel has higher entropy?
Denote by Vessel I the vessel with volume $V$, moles of water $N$, and moles of hydrogen $N'$. Denote by Vessel II the vessel with volume $2V$, moles of water $2N$, and moles of hydrogen $N'$.

Increasing the volume will increase the number of microstates available to the system, and hence also the entropy. Increasing the moles of water will increase the number of microstates available to the system, and hence also the entropy.

Both statements imply that Vessel II has the greater entropy.