A Thermally Isolated Sample of an Ideal Gas at a Fixed

A thermally isolated sample of an ideal gas at a fixed temperature is confined to one half of a container by an impermeable membrane.The other half of the container is evacuated.The membrane is then pierced and the gas is allowed to expand freely and to double its volume as shown.Which one of the following statements is true concerning this situation?

A) The process is reversible.
B) This is an isothermal process.
C) The entropy of the gas decreases.
D) The internal energy of the gas must decrease.
E) The temperature of the gas decreases to one-half of its original value.