
Two vessels \( A \) and \( B \) are connected via stopcock. The vessel \( A \) is filled with a gas at a certain pressure. The entire assembly is immersed in water and is allowed to come to thermal equilibrium with water. After opening the stopcock the gas from vessel \( A \) expands into vessel \( B \) and no change in temperature is observed in the thermometer. Which of the following statement is true?