It is 5.763J/K*kg. You can use the Omnicalculator tool Entropy or do as follows:
Use the change in entropy formula: ΔS = n * R * ln(V2/V1) considering n as the ideal gas moles equal to 1.
Notice that V2/V1 equals two because we are doubling the volume. Also, R is the ideal gas constant.
The result will be 5.763J/K*kg.
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